Si diffusion behavior during laser welding-brazing of Al alloy and Ti alloy with Al-12Si filler wire

Si diffusion behavior during laser welding-brazing of Al alloy and

Ti alloy with Al-12Si filler wire

CHEN Shu-hai(? ?), LI Li-qun( ?), CHEN Yan-bin(? ), LIU De-jian( )

State Key Laboratory of Advanced Welding Production Technology,

Harbin Institute of Technology, Harbin 150001, China

Received 11 June 2008; accepted 9 July 2009

Abstract: In laser welding-brazing of Al alloy (5A06) and Ti alloy (Ti-6Al-4V) with rectangular CO2 laser spot and with Al-12Si filler wire, element Si enriches at the interface between Ti substrate and the filler metal. It is found that the Si diffusion behavior has a significant effect on the formation of interfacial intermetallic compounds. To analyze the Si diffusion behavior, a model for the prediction of the chemical potential for ternary alloy was established. According to the calculated results of the influence of the element content and temperature in Ti-Al-Si system on Si chemical potential, the diffusion behavior of Si element was analyzed for Ti dissolution and melting mode, which presents a good agreement with the experimental data. Further, formation mechanism of the interfacial intermetllic compound was clarified.

Key words: laser welding-brazing; diffusion behavior; chemical potential; interfacial reaction

1 Introduction

In aircraft industry, hybrid structures of titanium and aluminum alloys could offer advantages in comparison with conventional materials[1í2]. The performances of Ti and Al have great differences in crystal microstructure, melting point, heat conductivity, coefficient of linear expansion, etc., so the joining of Al alloy to Ti alloy is difficult when applying the traditional fusion method. The dissimilar combination of titanium and aluminum has been realized by diffusion welding[3í4], vacuum brazing[5í6], friction welding[7] and explosion welding[8]. However, above welding methods are restricted by joint configuration or vacuum condition. In additional, low mechanical strength for the joints is another problem for these methods.

A key issue encountered in joining aluminum to titanium is the formation of interfacial intermetallic phases, which depends on the process related temperatureítime cycles. Due to its high energy density and cooling velocity, laser is suitable as the heat source of the controlling interfacial reaction in joining Al to Ti. To achieve laser joining of Al alloy to Ti alloy, while fusion joint is formed by melting aluminum and filler wire Al-12Si, brazing joint is formed by molten filler and solid titanium. Therefore, a reliable joining could be achieved with this method called “laser welding-brazing” by controlling effectively the interfacial reaction. Previous works indicated that good results of the welding are obtained and tensile strength of the joints can exceed that of most Al alloys[9í10].

Compared with brazing and diffusion-bonding, complex metallurgical reaction and diffusion process of elements appear due to fast heating and cooling velocities of the laser welding at the interface. It is found that both modes of Ti melting and dissolution, which depend on the heat input, exhibited in welding-brazing. In addition, the diffusion behavior of Si element has significant influence on interfacial reaction mechanism. Therefore, according to established prediction model of the chemical potential for the Ti-Al-Si system, the effect of the element content and temperature on Si chemical potential was analyzed. Further, Si diffusion behavior and interfacial reaction mechanism in both modes of Ti melting and dissolution were clarified.

2 Experimental

Non-uniform heating and small heating area are

Foundation item: Project(50275036) supported by the National Natural Science Foundation of China Corresponding author: CHEN Shu-hai; Tel: +86-451-86415506; E-mail: shchenhit@https://www.wendangku.net/doc/da12253542.html, DOI: 10.1016/S1003-6326(09)60098-4

CHEN Shu-hai, et al/Trans. Nonferrous Met. Soc. China 20(2010) 64í70 65

disadvantageous to melt stably filler wire and wet base metal. Therefore, laser beam was modulated to rectangular spot (focal spot size of 2 mm h4 mm) by the integral mirror to get more uniform energy distribution. To improve further the spreadablity, V-shape groove with 45? angle was fabricated on base metal. Double shielding gas argon was used at both sides of workpiece to avoid the oxidation of liquid metal. The laser beam irradiated the workpiece vertically, and there was focal spot position at the top surface of the workpiece during laser joining. The angle of 30? between the filler wire and the workpiece was selected. Filler wire was fed in front of the laser beam, as shown in Fig.1. To decrease the difference of heat conductivity and the reflectance of Ti and Al, the offset of laser beam toward Al metal base was set as 0.4 mm.

Fig.1 Schematic of laser joining Ti alloy to Al alloy

Ti-6Al-4V and 5A06 Al alloy plates with thickness of 1.5mm were selected as the laser joining materials. The Ti alloy is composed of Al(5.5%í6.8%), V(3.5%í4.5%) (mass fraction) and balance Ti; the 5A06 Al alloy is composed of Mg(5.8%í6.8%), Si(0.4%), Mn(0.5%í0.8%), Fe(0.4%), Zn(0.2%) (mass fraction) and balance Al. And the filler wire with the diameter of 2 mm is composed of Si(12%), Fe(0.8%), Cu(0.3%), Zn(0.2%) (mass fraction) and balance Al.

In this study, standard grinding and polishing sample preparation procedures were used and solutions of 1%HF, 1.5%HCl, 2.5%HNO3 and 95%H2O were used to etch samples. The microstructures of the joint were observed by metallographic microscope and scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectrometer (EDS) for chemical constitution analysis. The crystal phases of the reaction layer were identified by microbeam X-ray diffractometer, which has advantage of analyzing phase composition in minimum diameter of 50 ?m.

3 Results and discussion

3.1 Interfacial microstructure in Ti/Al joints

Fig.2 shows typical cross-section morphology of dissimilar Ti/Al laser welding-brazing joint. It is clear that welding joint has been formed by Al alloy and filler metal, and brazing joint has been formed by Ti alloys and filler metal. According to the observation of interfacial microstructure, there are two joining modes at the interface of Ti/filler metal, i.e., Ti dissolution mode formed by the dissolution of Ti substrate with low heat input and Ti melting mode formed by slight melting of Ti substrate with high heat input.

Under the condition of low heat input, SEM photograph of interfacial microstructure is shown in Fig.3. According to the results of the microbeam XRD,

Fig.2 Typical cross-section morphology of dissimilar Ti/Al laser welding-brazing joint

Fig.3 Interfacial microstructure (a) and distribution of elements Ti, Al, Si, Mg and V (b) with dissolution mode

CHEN Shu-hai, et al/Trans. Nonferrous Met. Soc. China 20(2010) 64í70 66

SEM and EDS, there are two reaction layers with discontinuous Ti(Al, Si)3 and continuous Ti5Si3 at the interface. Intermetallic Ti(Al, Si)3 reaction layer exhibits discontinuous serrate shape. Very thin Ti5Si3 reaction layer lies between Ti(Al, Si)3 layer and Ti alloy substrate. Fig.3(b) shows the distribution of elements Ti, Al, Si, Mg and V by EDS line scanning at the interface. It is obvious that element Si enriches at the interface between Ti substrate and the filler metal.

With increasing heat input, Ti alloy substrate is melted slightly at the interface. Accordingly, the joining of Al-12Si filler and Ti base metal becomes melting mode. Interfacial microstructure of the joining with melting mode is complex, as shown in Fig.4(a). The thickness of continuous reaction layer increases obviously. According to the results of microbeam XRD and EDS, interfacial microstructure is divided into five layers, i. e. solid-state phase changed reaction layer with Ti3Al and precipitation Ti5Si3 (?), eutectic reaction layer with TiAl and Ti5Si3(?), hypoeutectic reaction layer with Ti5Si3 and primary TiAl (?), hypereutectic reaction layer with primary Ti5Si3 and TiAl (?) and discontinuous reaction layer with Ti(Al, Si)3(?). Granular Ti5Si3 compounds are surrounded by intermetallic phase TiAl in hypereutectic reaction layer. In addition, little Ti5Si3 particles are precipitated in solid-state phase changed reaction layer close to fusion

Fig.4 Interfacial microstructure (a) and distribution of elements Ti, Al, Si, Mg and V (b) with melting mode line, as shown in Fig.5. Fig.4(b) shows the distribution of elements Ti, Al, Si, Mg and V by EDS line scanning at the interface. Similarly, element Si enriches at the interface between Ti substrate and the filler metal.

Fig.5 Morphology of Ti5Si3 precipitation particles of solid-state phase changed reaction layer in melting mode

The analysis of interfacial microstructure of Ti/Al dissimilar joints shows that Si element participates in formation of the compound Ti7Al5Si12 and becomes solutes replacing Al atoms in TiAl3 for dissolution mode. For Ti melting mode, Si participates in eutectic, hypoeutectic and hypereutectic reaction and the precipitation of Ti5Si3 in solid reaction layer. In nature, interfacial reaction mechanism and product formation are affected by the Si diffusion behavior. The Si diffusion behavior will be analyzed from the view of Si chemical potential to explain interfacial mechanism.

3.2 Chemical potential prediction model of ternary

alloys

During diffusing of the elements, gradient of the chemical potential is a driving force. Element will diffuse to the place where chemical potential is low. Generally, it is difficult to directly calculate or measure the chemical potential. So far, no accurate calculation or measurement of the chemical potential has been reported. Therefore, a model for the prediction of the chemical potential for ternary alloy system is established to analyze the influence of the element content and temperature on Si chemical potential.

As it is known, partial molar free energy, i.e., chemical potential is expressed by

i

i

G

x

P

w

w

(1)

In fact, free energy G of real solution is equal to the summation of ideal solution free molar energy G I and excess molar free energy G E, namely,

G= G I+ G E(2) The mixed free energy of ideal solution is expressed by I0I***

(ln ln ln)

i i j j k k

i i j j k k

G G G x G x G x G

RT x x x x x x

'

(3) where *i G,*j G and *k G are molar free energies of pure

CHEN Shu-hai, et al/Trans. Nonferrous Met. Soc. China 20(2010) 64í70 67

component i , j , k , respectively; and x is the molar fraction of the component.

The calculation of the excess molar free energy G E is a key issue in the established model. It is impossible that G E of ternary system is calculated accurately by traditional thermodynamic theory. Thus, Toop equation is used to evaluate the excess free energy of ternary alloys by using that of binary alloys. In ternary system i -j -k , where j and k are symmetry components and i is asymmetry component, according to excess molar free

energies of binary alloys E ij G , E jk G and E ik G , the

excess molar free energy G E of ternary system alloys is obtained from Toop equation[11í12]: E E E

2E 1(,1)(,1)111 (1)(,)11j

i j ij i i ik i i i

i

j i j

i jk

i i

x x x G G x x G x x x x x x x x G x x

(4)

In this way, questions are used to calculate the

excess molar free energy G E of ternary system to

translate the excess molar free energy E

ij G , E jk G and E

ik G of binary system. Under the condition of changeless temperature, free energy of binary system is

E E m ij ij G H T S ' ' (5) where ij H ' and E m S ' are solution enthalpy and excess entropy of binary system, respectively.

Based on the relationship of excess entropy with solution enthalpy established by TANAKA et al[13], there is

E m m,m,(1/1/)/14ij i j S H T T ' (6)

where T m, i and T m, j are melting points of components i and j , respectively.

Therefore, excess molar free energy of binary alloys becomes

E m,m,[1(1/1/)/14]ij ij i j G H T T T ' (7)

According to Eq.(7), the excess free energy E ij G of binary system is calculated by solution enthalpy ?H ij . Further, the excess free energy G E of ternary system is obtained by Eq.(4). Besides elements O, S, Se and Te, for any two elements i and j , the solution enthalpy expression is shown by MIEDEMA model of solution enthalpy[14]:

,2/32/3[1()][1()]

[1()][1()]

i j ij i i j i j j j i j i i i i j i j j j j i j i H f x x x x x V x x V x P I I P I I P I I P I I ' (8a)

2/32/31/322

WS 1/31

1/31WS WS 2[/()()(/)]

()()

i j ij i pV V q p n a r p f n n I ' '

(8b)

where x is the molar fraction of element; ? is the

electronegativity; V is the molar volume; n WS is the electron density; and q , r , ?, a , p are experimential constants, whose physical significances and values are described in detail elsewhere[14].

Therefore, according to Eqs.(1)í(8), chemical potential prediction model of ternary alloys is established. The mixed free energy of Ti-Al-Si ideal solution is obtained by Eq.(3) and the excess free energy G E of this system is obtained according to Eqs.(4)í(8). Finally, Si chemical potential of this system is calculated by Eqs.(1) and (2).

3.3 Analysis of Si diffusion behavior at interface

during laser joining

3.3.1 Calculation of Si chemical potential in Ti-Al-Si

system

In this study, the melting points of Ti and Al are around 1 900 and 900 K, respectively. According to prediction model of ternary alloy, Si chemical potential dependent on molar fraction of Ti and Si is calculated for dissolution mode (1 000 K) and melting mode (2 000 K), as shown in Fig.6. Therefore, Si diffusion behavior is analyzed according to relationship of Si chemical potential with some factors, for example, element content and temperature.

3.3.2 Si diffusion behavior for Ti dissolution mode

In this study, there is 12% Si (mass fraction) in filler

Fig.6 Si chemical potential dependent on molar fraction of Ti

and Si in dissolation mode (1 000 K) (a) and melting mode (2 000 K) (b)

CHEN Shu-hai, et al/Trans. Nonferrous Met. Soc. China 20(2010) 64í70 68

Ai-12Si (molar fraction of 0.116). This means that ratio of Al to Si in liquid filler is always remained during Ti dissolution. Thus, the influence of Ti molar fraction on Si chemical potential was analyzed during laser joining under this ratio.

The relationship curves of Si chemical potential ?(Si) with Ti molar fraction x(Ti) was calculated, as shown in Fig.7. It is clear that critical point of Ti molar fraction is 0.5 at almost all temperatures. With increasing Ti molar fraction, Si chemical potential decreases when this fraction is lower than 0.5 and increases when it is higher than 0.5. As shown in Fig.7, Si chemical potential tends to decrease with increasing temperature. However, the influence of Ti molar fraction is far higher than that of the temperature on Si chemical potential. Therefore, the attention is focused on the influence of the Ti content distribution on Si chemical potential.

Fig.7 Relationship curves of Si chemical potential with Ti molar fraction

In Ti dissolution mode, element distribution between A and B points in Fig.3(a) is shown in Table 1. It is obvious that Ti molar fraction is lower than 0.5 in Table 1. This means that Si chemical potential decreases with increasing Ti molar fraction during joining for Ti dissolution mode. In liquid filler near the interface, Ti content is the highest, which leads to the reduction of Si chemical potential. Therefore, Si atom in liquid filler diffuses to the interface during laser joining, and then Si gathering phenomena appear at the interface.

During interfacial reaction, Si gathering phenomena and Ti dissolution induce the formation of Si-rich compound Ti7Al5Si12 at the interface. The formation of this compound wastes a number of Si atoms, which induces the reduction of Si content at the interface. Therefore, intermetallic TiAl3 is formed in the form of crystallization. Considering the gathering phenomena of Si atoms, up to 15% Al can be replaced by silicon in TiAl3 lattice structures due to the adjacent atomic radii, and it can be commonly written as Ti(Al, Si)3[15]. Table 1 Element content distribution in reaction layer for Ti dissolution mode

Distance/?m x(Mg)/%x(Al)/% x(Si)/% x(Ti)/%x(V)/%

8.02 1.12 59.07 9.38 28.7 1.73

8.2 1.28

58.6

8.81

30.980.33

8.39 0.45

61.35

8.83

28.960.41

8.58 0.78

60.28

11.66

25.17 2.11

8.76 1.36

60.22

11.15

26.5 0.78

8.95 0.54

60.08

10.99

28.390

9.13 0.89

62.14

11.79

25.180

9.32 1.44

66.23

9.79

21.670.87

9.51 1.11

67.03

8.65

23.210

9.69 0.91

67.75

6.67

23.860.8

3.3.3 Si diffusion behavior for Ti dissolution mode

In the case of melting mode, Ti substrate is melted slightly at the interface due to high heat input, which means contact of liquid Ti with liquid filler. Thus, smart diffusion process appears also in liquid Ti besides liquid filler. Two zones with liquid filler and liquid Ti at the interface are divided to analyze Si diffusion behavior,

as shown in Fig.8.

Fig.8 Schematic diagram of diffusion process for melting mode In liquid filler zone, the Si diffusion behavior is similar with dissolution mode. Si chemical potential decreases in liquid filler due to the diffusion of the liquid

Ti to the filler. Thus, Si atom will enrich at the interface from liquid filler.

In the liquid Ti zone, the Si chemical potential,

?[Si(Al-12Si)], in liquid filler (x(Ti)=0) is far higher than

?[Si(Ti)] in liquid Ti (x(Ti)=1), as shown in Fig.8. This indicates that the Si and Al atoms diffuse strongly to liquid Ti from filler due to the drive of the chemical potential gradient. Clearly, the ratio of Al or Si in liquid

Ti is different with liquid filler at early stage of the diffusion. Thus, Si chemical potential is influenced by Si and Ti contents. Fig.9 shows the relationship of Si chemical potential with Si content under the condition of

the same Ti molar fraction. As shown in Fig.9, Si chemical potential decreases with the reduction of Si

CHEN Shu-hai, et al/Trans. Nonferrous Met. Soc. China 20(2010) 64í70 69

molar fraction in the case of the same Ti content for Ti-Al-Si ternary system. Under the condition of the same Si content, Si chemical potential decreases with increasing Ti molar fraction. It is shown that Si atom tends to diffuse to the zone with low Si and high Ti molar fraction for Ti-Al-Si ternary system. During welding, Si content decreases and Ti content increases with increasing distance from the interface in liquid Ti. Therefore, Si atom diffuses to inner zone of liquid Ti during laser joining for melting mode.

Fig.9 Influence of Si molar fraction on Si chemical potential for same Ti content

In addition, Si and Ti contents in liquid Ti increase continuously with progress of the diffusion. Finally, the ratio of Al or Si in liquid Ti is the same with that in liquid filler because the bulk of liquid filler is far larger than that of liquid Ti. Therefore, Si chemical potential can reach the minimum value, as shown in Fig.7, when Ti molar fraction is around 0.5. Element distribution between C and D points in Fig.4(a) is shown in Table 2. It is obvious that Ti molar fraction is around 0.5 and ratio of Al or Si is close to that in liquid filler, which indicates that prediction model of chemical potential is proper.

There is complex metallurgical reaction at the interface during the diffusion. According to above five

Table 2 Element distribution in reaction layer for Ti melting mode

Distance/?m x(Mg)/% x(Al)/%x(Si)/% x(Ti)/%x(V)/%

15.15 1.3 41.79 3.35 51.03 2.52

15.35 1.75 38.19 3.94 52.21 3.91

15.55 1.01 41.68 3.02 50.14 4.15

15.75 0.93 42.84 3.44 51.17 1.61

15.95 1.69 39.32 6.41 50.73 1.86

16.15 0.76 40.24 4.21 49.51 5.27

16.35 1.44 39.46 4.37 50.38 4.35

16.55 2.11 40.49 3.21 51.66 2.52

16.75 2.11 39.51 4.42 49.25 4.71

16.95 1.54 39.92 4.24 49.7 4.61 layers in melting mode, corresponding interfacial reaction is analyzed as follows.

In zone ?, the solid-state phase changes occur in solid Ti alloy substrate near fusion line due to Si and Al diffusion. The solid-state phase changed reaction layer with Ti3Al and precipitation Ti5Si3 is formed.

In zone ?, eutectic reaction appears in melting Ti alloy near fusion line: L?TiAl+Ti5Si3. The filamentous eutectic reaction layer with Ti5Si3 and TiAl is formed.

In zone ?, Ti5Si3 as primary phase is formed due to high melting point of Ti5Si3 and strong combining capability of Si with Ti[16]. Hypereutectic reaction layer with TiAl and primary Ti5Si3 appears in this zone.

In zone ?, because a mass of Si atoms are expended by formation of Ti5Si3 in hypereutectic reaction layer (zone ?), surrounding Si should diffuse to around reaction zone of Ti5Si3 formation, which induces appearance of poor Si zone between zone ? and ?. Therefore, hypoeutectic structure of Ti5Si3 and primary TiAl is formed in this zone.

In the zone ?, with the decrease of temperature, serration-shape reaction layer consisting of Ti(Al, Si)3 forms in crystallization. The formation mechanism of Ti(Al, Si)3 layer is the same as dissolution mode.

4 Conclusions

1) In laser joining of Al alloy to Ti alloy, Si element diffuses to the interface and enriches there with the mode of Ti dissolution or melting. It is found that Si diffusion behavior plays an important role in forming those interfacial compounds.

2) Chemical potential prediction model of the ternary alloys is established based on MIEDEMA model of solution enthalpy. The influence of Ti molar fraction and temperature on Si chemical potential is analyzed according to calculated results. It is found that the influence of Ti molar fraction is far higher than that of the temperature on Si chemical potential. The minimum value of Si chemical potential is approximate 0.5 of Ti molar fraction, which presents a good agreement with experimental data.

3) In the case of Ti dissolution mode, the dissolution of Ti alloy in liquid filler induces the reduction of the Si chemical potential. This causes the phenomenon of Si element gathering at the interface. In the case of Ti melting mode, element Si not only gets together at the interface, but also further diffuses to liquid Ti due to slight melting of Ti substrate.

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(Edited by YANG Bing)

激光选区烧结

激光选区烧结 1 .工艺过程原理 激光选区烧结(Selected Laser Sintering , SLS )采用CO ：激光器对粉末材料(塑料粉、陶瓷与粘结剂的混合粉、金属与粘结剂的混合粉等)进行选择性烧结，是一种由离散点一层层堆积成三维实体的工艺方法，其工艺过程原理如图8 一7 所示，典型设备如美国DTM 公司的Sinterstation 一2500 型粉末材料激光烧结站。 激光选区烧结在开始加工之前，先将充有氮气的工作室升温，并保持在粉末的熔点以下。成形时，送料筒上升，铺粉滚筒移动，先在工作平台上铺一层粉末材料，然后激光束在计算机控制下按照截面轮廓对实心部分所在的粉末进行烧结，使粉末熔化继而形成一层固体轮廓。第一层烧结完成后，工作台下降一截面层的高度，再铺上一层粉末，进行下一层的烧结，如此循环，形成三维的原型零件。最后经过5 ? 10h 冷却，即可从粉末缸中取出零件。未经烧结的粉末能承托正在烧结的工件，当烧结工序完成后，取出零件，未经烧结的粉末基本可自动脱掉，并重复利用。因此，SLS 工艺不需要建造支撑，事后也不要为清除支撑而烦恼。 2 . SLS 优缺点和应用范围 SLS 快速原型技术的优点是： l )与其他工艺相比，能生产最硬的模具。 2 )可以采用多种原料，例如绝大多数工程用塑料、蜡、金属、陶瓷等。

3 )零件构建时间短，每小时高度可达到lin 。 4 )无需对零件进行后矫正。 5 )无需设计和构造支撑。 SLS 快速原型技术的缺点是： l )在加工前，这种工艺仍须对整个截面进行扫描和烧结，加上要花近2h 的时间将粉末加热到熔点以下，当零件构建之后，还要用5 ? 10h 冷却，然后才能将零件从粉末缸中取出，成形时间较长。 2 )表面粗糙度受粉末颗粒大小及激光点的限制。 3 )零件的表面一般是多孔性的，在烧结陶瓷、金属与枯结剂的混合粉并得到原型零件后，为了使表面光滑，必须将它置于加热炉中，烧掉其中的枯结剂，并在孔隙中渗人填充物，其后处理较为复杂。 4 )需要对加工室不断充氮气以确保烧保结过程的安全性，加工的成本高。 5 )该工艺产生有毒气体，污染环境。 激光选区烧结工艺适合成形中小件，能直接得到塑料、陶瓷或金属零件，零件的翘曲变形比液态光固化成形工艺要小。激光选区烧结快速原型工艺适合于产品设计的可视化表现和制作功能测试零件。由于它可采用各种不同成分的金属粉末进行烧结，进行渗铜后置处理，因而其制成的产品可具有与金属零件相近的力学性能，故可用于制作EDM 电极、直接制造金属模以及进行小批量零件生产，激光选区烧结的最大优点是可选用多种材料.适合不同的用途。所制作的原型产品具有较高的硬度，可进行功能试验。 作者：环保空调https://www.wendangku.net/doc/da12253542.html, https://www.wendangku.net/doc/da12253542.html,

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3D打印SLS（选择性激光烧结）技术 内容来源网络，由“深圳机械展（11万㎡，1100多家展商，超10万观众）”收集整理！ 更多cnc加工中心、车铣磨钻床、线切割、数控刀具工具、工业机器人、非标自动化、数字化无人工厂、精密测量、数控系统、3D打印、激光切割、钣金冲压折弯、精密零件加工等展示，就在深圳机械展. 发展历史 SLS（选择性激光烧结工艺），该工艺是1989由美国德克萨斯大学C.R.Dechard 提出的，随后C.R.Dechard创立了DTM公司并于1992年发布了基于SLS技术的工业级商用3D打印机Sinterstation。 工艺原理 SLS利用粉末材料在激光照射下烧结的原理，由计算机控制层层堆结成型。SLS技术同样是使用层叠堆积成型，所不同的是，它首先铺一层粉末材料，将材料预热到接近熔化点，再使用激光在该层截面上扫描，使粉末温度升至熔化点，然后烧结形成粘接，接着不断重复铺粉、烧结的过程，直至完成整个模型成型。

工艺优点 ?可选材料种类多，价格较低。只要材料加热后粘度较低，基本就可以作为SLS 的材料。包括高分子、金属、陶瓷、石膏、尼龙等多种粉末材料。 ?工艺比较简单。该工艺按材料的不同可以直接生产复杂形状的原型、型腔模三维构建或部件及工具。 ?不需要支撑结构。未烧结的粉末即可作为支撑结构。 ?材料利用率高，因为不存在支撑结构和底座，所有材料均可利用。 ?精度高。一般受才种类和粉末颗粒的大小等因素影响，精度一般在 0.05mm-2.5mm之间。 ?变形率小 工艺缺点 ?表面粗糙。由于原材料是粉状的，原型建造是由材料粉层经过加热熔化实现逐层粘结的。 ?无法直接成型高性能的金属盒陶瓷零件，成型大尺寸零件时容易发生翘曲变形。?加工时间长。加工前，要有2小时的预热时间。零件构建后，要花5~10小时时间冷却，才能从粉末缸中取出。 ?由于使用了大功率激光器，除了本身的设备成本，还需要很多辅助保护工艺，整体技术难度大，制造和维护成本非常高。 产品应用 ?汽车领域的产品及结构验证：汽车挡板、后视镜、仪表盘、方向盘、车灯、座椅及把手等。

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间过长后会因为内应力释放而变形。对容易发生变形的地方设计支撑，表面质量一般。生产效率较高，运营成本较高，设备费用较贵。 能耗通常在8000瓦以上。材料利用率约100%。 SLS工艺又称为选择性激光烧结，由美国德克萨斯大学奥斯汀分校的C.R. Dechard于1989年研制成功。SLS工艺是利用粉末状材料成形的。将材料粉末铺洒在已成形零件的上表面，并刮平；用高强度的CO2激光器在刚铺的新层上扫描出零件截面；材料粉末在高强度的激光照射下被烧结在一起，得到零件的截面，并与下面已成形的部分粘接；当一层截面烧结完后，铺上新的一层材料粉末，选择地烧结下层截面。 SLS工艺最大的优点在于选材较为广泛，如尼龙、蜡、ABS、树脂裹覆砂（覆膜砂）、聚碳酸脂（poly carbonates）、金属和陶瓷粉末等都可以作为烧结对象。粉床上未被烧结部分成为烧结部分的支撑结构，因而无需考虑支撑系统（硬件和软件）。SLS工艺与铸造工艺的关系极为密切，如烧结的陶瓷型可作为铸造之型壳、型芯，蜡型可做蜡模，热塑性材料烧结的模型可做消失模。3.3 选择性激光烧结法(SLS) 选择性激光烧结法又称为选区激光烧结。它的原理是预先在工作台上铺一层粉末材料（金属粉末或非金属粉末），激光在计算机控制下，按照界面轮廓信息，对实心部分粉末进行烧结层层堆积成型。 一、选择性激光烧结工艺的最新研究进展与成果 SLS 工艺最初是由美国德克萨斯大学奥斯汀分校的Carl Deckard 于1989 年在其硕士论文中提出的。后美国DTM公司于1992 年推出了该工艺的商业化生产设备SinterSation。几十年来,奥斯汀

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激光选区烧结成形材料的研究和应用现状 曾锡琴1朱小蓉2 1．江苏电大武进学院，江苏常州，213161； 2．江苏工业学院机械系，江苏常州，213016 [摘要] 介绍了激光快速成形的原理及SLS对材料性能的要求，概括了激光选区烧结成形技术中各种材料的研究和应用现状，分析了SLS技术产业化存在的问题及可能解决的途径。 [关键词] 选择性激光烧结，材料，研究与应用 Research and Application Present Condition on the Materials of Selective Laser Sintering ZENG Xi-qin1ZHU Xiao-rong 1．Wujin TV University, Jiangsu Province, China; 2．Department of Mechanical Engineering, Jiangsu polytechnique university, Changzhou 213016 ,China) Abstract：In this article the principle of the selective laser sintering, the situation of the research and application on material by SLS are summarized. The existent problems and solving methods are discussed. Keywords: selective laser sintering, material，research and application 0．引言 SLS（selective laser sintering）作为快速原形制造技术的重要分支之一，是目前发展最快和应用最广的技术之一[1]。它和SLA、LOM构成激光快速成形技术的核心。与其它快速成形技术相比，SLS以选材广泛、无需设计和制造复杂支撑并且可直接生产注塑模、电火花加工电极以及可快速获得金属零件等功能性零件而受到了越来越广泛的重视。 1．激光选区烧结成形技术 SLS所用的激光有两种：CO2激光器和Nd：YAG激光器。大部分金属对CO2激光器的反射率比对Nd：YAG激光器的反射率大，不利于金属粉末对激光能量的吸收。在SLS系统中，激光束对任何粉末颗粒的作用时间都非常短，大约为几毫秒到几十毫秒，所以目前SLS技术大多采用液相烧结[2]，其材料一般由两种熔点相差明显的成分组成，高熔点成分称为结构材料，低熔点成分称为粘结剂。因此，从原则上讲所有受热能相互粘结的粉末材料或表面覆有热固（塑）性粘结剂的粉末都能用作SLS 材料。 2．国内外主要SLS成形材料及其应用现状 目前，SLS材料主要有塑料粉、蜡粉、尼龙、金属或陶瓷的包衣粉（或与聚合物的混合物）等。 2．1 有机材料 从理论上说，任何热塑性粉末均可采用SLS技术成形为任何复杂形状的制件。目前常见的有：（1）蜡粉，传统的熔模精铸用蜡（烷烃蜡、脂肪酸蜡等），蜡模强度较低，难以满足精细、复杂结构的铸件的要求，且成形精度差，所以DTM研制了低熔点高分子蜡的复合材料；华北工学院采用化学合成法，开发了以氧化聚乙烯为主要成分的复合精铸蜡粉（PCP1），其成形件经过简单的后处理（清粉、涂液）即可达到精铸蜡模的要求[1]。 （2）聚苯乙烯（PS） 聚苯乙烯受热后可熔化、粘结，冷却后可以固化成形，而且该材料吸湿率小，收缩率也较小，其成形件浸树脂后可进一步提高强度，主要性能指标可达拉伸强度≥15Mpa、弯曲强度≥33 Mpa、冲击强度≥3Mpa，可作为原形件或功能件使用；也可用做消失模铸造用母模，生产金属铸件，但其缺点是必须采用高温燃烧法(>300℃)进行脱模处理，造成环境污染。因此，对于PS粉原料，针对铸造消失 1