7075铝合金搅拌摩擦焊研究
7075铝合金搅拌摩擦焊研究
沈 洋 王快社 吕 爽 孙 鹏(西安建筑科技大学冶金工程学院)
摘 要 使用搅拌摩擦焊对8mm 厚的70752T7351铝合金进行了单道平板对接。结果表明,在工艺参数为搅拌头旋转速度为1180r/min 、焊接速度为3715mm/min 时,可获得较好的接头,抗拉强度达到390MPa ,是母材强度的78%;70752
T7351铝合金搅拌摩擦焊接头微观组织为典型的搅拌摩擦焊接头组织,焊核区为细小的等轴晶,晶粒大小为6～7μm ,母材
组织中的强化相在此区域消失;接头显微硬度值分布趋势沿焊缝中心两侧基本对称,热机影响区2热影响区过渡区及焊核区硬度低于母材,是焊件的薄弱环节。
关键词 搅拌摩擦焊;微观组织;7075铝合金;平板对接焊中图分类号 T G 45711;T G 465 文献标志码 A 文章编号 1001-2249(2007)02-0145-03
收稿日期:2006-11-20
基金项目:陕西省国际科技合作重点项目计划(2005KW 220);陕西省科技厅科技计划项目(2003K072G8)
第一作者简介:沈洋,男,1981年出生,硕士研究生,西安建筑科技大学冶金工程学院,西安(710055),电话:029*********,E 2mail :shenyang660@https://www.wendangku.net/doc/b18131775.html,
搅拌摩擦焊(FSW )[1]是英国焊接研究所发明的一种固相连接新工艺,具有连接温度低、焊后残余应力小、接头性能高等一系列优点[2～8],在航空航天、造船、汽车等领域,尤其是高强铝合金的连接方面具有广阔的应用前景。7075铝合金是一种可热处理强化的Al 2Mg 2Zn 2Cu 系超硬铝合金材料,熔铸方便,成形性好,经轧制能获得比较理想的板材,通过固溶及回归再时效处理,可使它获得优良的综合性能。70752T7351铝合金广泛应用于航空航天工业,是典型的高强轻质材料。目前该类合金的焊接主要采用M IG 焊,焊后焊缝中容易出现焊接变形和气孔,残余应力较大,且对应力腐蚀敏感,不能充分发挥材料的性能。本课题选取8mm 厚的70752T7351铝合金进行单道平板对接搅拌摩擦焊,研究该合金焊件的组织与力学性能,具有重要的实用价值。
1 试验方法
焊接试验使用的材料为8mm 厚的70752T7351铝
合金轧制板材,焊件尺寸为160mm ×40mm ×8mm 。70752T7351铝合金板的化学成分与室温力学性能见表1与表2。试验使用搅拌头材料为高速钢,搅拌头轴肩直径为24mm ,搅拌针直径为8mm ,高为7mm 。试验时,将铝合金板材按规定尺寸加工好,采用平板对接方式进行搅拌摩擦焊接。焊接前用专用夹具将两块板沿与板面垂直方向夹紧,以保证两板连接处的缝隙结合紧密。焊接设备采用改装过的X53K 型立式升降台铣床。焊接工艺参数为:搅拌头旋转速度为950～1200r/min ,搅拌头沿焊缝方向的焊接速度为3715～60mm/min 。焊接后对不同组别中成形良好的焊接接头进行硬度试验并制作金相试样观察组织形貌。腐蚀剂
成分(体积分数)为:10%的HF 、15%的HCl 、75%的H 2O ,腐蚀时间为45s 。在CSS 24100电子万能拉伸机上进行拉伸试验,在MM5金相光学显微镜观察微观组织,使用M HV 22型显微硬度计进行显微硬度试验。
表1 7075铝合金化学成分
%
w B
Mg Zn Cu Cr Fe Si Ti Al
211～219511～611112～2.00118～0128<015<014<012余量
表2 70752T 7351室温力学性能
σb /MPa
σ012/MPa
δ/%
HV 505
435
13
155
2 试验结果与分析
2.1 工艺参数对焊件抗拉强度的影响
图1为试验工艺条件下7075铝合金搅拌摩擦焊接头抗拉强度。从图1可见,在未进行焊后热处理的情况下,搅拌头旋转速度为1180r/min 、焊接速度为3715mm/min 时,焊件的抗拉强度最好,为390M Pa 左右,达到母材强度的78%,证明70752T7351铝合金板搅拌摩擦焊接头力学性能较好
。
图1 焊件的抗拉强度
轻有色合金特种铸造及有色合金 2007年第27卷第2期
2.2 焊件表面形貌
试验结果表明,
在合理的工艺参数下可获得表面成
形良好的70752T7351铝合金搅拌摩擦焊接头(见图2)。但由于7075铝合金母材有较厚的氧化膜,导致焊件回退侧易形成翻边,需焊后机械去除
。
(a )
焊件上表面
(b )焊件下表面
图2 7075铝合金搅拌摩擦焊接头表面形貌
2.3 焊缝的宏观形貌
图3是70752T7351铝合金搅拌摩擦焊接头横断面
宏观形貌照片,其搅拌头转速为1180r/min ,焊接速度为3715mm/min 。由图可知,在此工艺参数下得到的焊缝连接较好,无焊接缺陷。70752T7351铝合金搅拌摩擦焊接头具有搅拌摩擦焊接头典型的宏观形貌:图3中A 区为焊核区(WN ),材料在该区发生了剧烈的变形;B 区为热机影响区(TMA Z ),材料在该区也有变形迹象,但由于搅拌磨头的旋转作用,左右两边的流线方向有所不同,A 区、B 区宽度与搅拌头轴肩直径基本相同,为24mm 左右;C 区为热影响区(HA Z )与母材组织(BM ),从图中可以看到,B 区、C 区有较明显的分界
。
图3 70752T7351铝合金搅拌摩擦焊接头横断面
2.4 焊缝的微观形貌
70752T7351铝合金母材组织为板条状轧制组织(见图4)。70752T7351铝合金的主要强化机制为析出
强化,合金的强度主要由基体析出相的大小、数量和弥
散度决定。金相照片中弥散分布的黑色颗粒是含铁、硅的强化相,这些强化相主要是Mg 32(Al ,Zn )49和Mg (Zn2,AlCu )[9]。
图5a 为70752T7351铝合金搅拌摩擦焊接头热机
图4 70752T7351铝合金母材组织
影响区组织,此区域是母材组织与焊核区组织的过渡区
域。材料在这一区域中部分发生了塑性变形与动态再结晶,转变成细小的等轴晶,此区域晶粒大小约为15～30μm 。同时材料组织中依然存在少量强化相颗粒。图5b 为70752T7351铝合金搅拌摩擦焊接头焊核区组织,此区域由于受到搅拌头强烈的机械搅拌,以及摩擦产生的局部高温作用,组织经历了完全动态再结晶,全部转变为细小的等轴再结晶组织,晶粒大小为6～7μm 。在母材组织中出现的黑色强化相颗粒,在焊核
组织中并未出现,表明焊接过程中焊核区的温度超过了
强化相的固溶温度,即可能达到了450℃以上[10～12],这一温度值与试验的数值模拟结果也是相符的。由于焊核区组织与其它区域存在的明显差别,导致了图3中所示的A 区与B 区、C 区域在腐蚀后存在明显的亮度差别
。
(a )
TMAZ
(b )WN
图5 70752T7351铝合金搅拌摩擦焊接头焊缝组织
2.5 焊缝的显微硬度
图6是70752T7351铝合金搅拌摩擦焊接头的显微硬度分布图。由图可知,TMA Z/HAZ 过渡区及焊核区硬度低于母材,这是由于TMA Z/HAZ 过渡区内由于温度的作用,可能使弥散分布的细小强化相发生了集聚,材料出现了过时效;在焊核区组织中强化相已全部
特种铸造及有色合金 2007年第27卷第2期
固溶,没有类似于母材组织中的强化相(图4中黑色颗粒)分布(见图5b),使得硬度降低。显微硬度值分布趋势沿焊缝中心两侧基本对称,但硬度值不对称,这是由于在焊接过程中,搅拌头焊针旋入侧和旋出侧的材料的变化不一致所致。焊缝两侧材料的塑性流动属非稳定流场,在搅拌头焊针旋入侧,“塞积”现象较严重,组织致密,晶粒变形较大,畸变能增加,加工硬化现象较焊针旋
出侧显著,因而在进行硬度试验时会有上述现象出现
。
图6 70752T7351铝合金搅拌摩擦焊接头显微硬度
对于无宏观缺陷的搅拌摩擦焊件,由于合金成分没有发生变化,其强度特性和断裂的位置只与微观硬度有关。因此,焊缝TMA Z/HAZ的过渡区及焊核区是70752T7351铝合金搅拌摩擦焊件的薄弱环节。
3 结论
(1)成功实现了8mm厚70752T7351铝合金的搅拌摩擦焊,最佳工艺参数为:搅拌头旋转速度为1180r/min、焊接速度为3715mm/min;抗拉强度达到390M Pa,是母材强度的78%。
(2)70752T7351铝合金搅拌摩擦焊接头微观组织为典型的搅拌摩擦焊接头组织,分为焊核区、热机影响区、热影响区及母材区;其中焊核区为细小的等轴晶组织,平均晶粒大小为6～7μm,母材组织中的强化相在此区域消失。
(3)70752T7351铝合金搅拌摩擦焊接头显微硬度值分布趋势沿焊缝中心两侧基本对称,TMAZ/HAZ过渡区及焊核区硬度低于母材,是焊件的薄弱环节。
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7075铝合金搅拌摩擦焊研究 沈 洋等
t he compo sites becomes finer and finer.In addition, t he creation of new p hase in t he heat t reated compos2 ites can be found wit h increasing in heat t reated tem2 perat ure and cooling rate,which is att ributed to t he increase of cooling rate resulting in t he decrement of eutectic growt h temperat ure.
K ey Words:Z L108Alloy,Aluminosilicate Short Fiber, Composites,H eat T reatment,Cooling R ate Microstructure and Properties of Al2O3/Cu Composites Prepared by Internal Oxidation of Cu2Al Alloy Zha ng X i ao na n1,Zhao Do ngmei1,Do ng Qiming2,Liu Ping1,Ren Fengzha ng1,Ti a n Baoho ng1(1.Henan U2 niversity of Science and Technology,L uoyang,China;
2.Henan University of Technology,L uoyang,Chi2 na)2007,27(2)142～144
Abstract Al2O3/Cu composites were prepared by inter2 nal oxidation of Cu2Al sheet at900℃to investigate t he microst ruct ure and properties of t he compo sites, in which t he Cu2O powder was used as oxidizer.The result s indicate t hat t he Al2O3particles are dispersive2 ly dist ributed in t he diff usion zone.The grain size in surface and inner of diff usion zone is sharply different, finer in t he surface t han in t he inner.The micro2hard2 ness of surface of diff usio n zone can be imp roved due to Al2O3disperoids st rengt hening Cu mat https://www.wendangku.net/doc/b18131775.html,2 pared wit h solid soluted Al atom in Cu mat rix,t he Al2O3disperoids has slightly affected t he elect ron dif2 f raction,resulting in t he increase of elect ric conductiv2 ity after Al2O3precipitation.Wit h increase of deform2 ation rate of Al2O3/Cu sheet in case of cold working, t he tangle of Al2O3disperoids wit h dislocation be2 comes worse and worse.
K ey Words:Al2O3/Cu Composites,Internal Oxidation, Electric Conductivity,Micro2hardness
7075Aluminum Alloy in Stirring Frictional Welding Shen Ya ng,Wa ng K uai she,LüShua ng,Sun Peng (College of Metallurgy Engineering,Xi’an University of Architect ure and Technology,Xi’an,China)2007, 27(2)145～147
Abstract Stirring f riction welding was employed in t he butt welding of t he7075Al alloy wit h8mm t hickness in single pass.The desirable joint wit h tensile st rengt h of390MPa can be achieved wit h t he rotating speed of stirring joint at1180r/min and welding speed at3715mm/min,which is78%of t hat of t he matrix materials.The micro struct ure of t he joint exhibit s typical stirring friction joint st ruct ure,consisting of fine equiaxed grain wit h size of6～7μm and finding t he absence of enhancing p hase in t he welding nugget.Mi2 cro2hardness of t he joint is symmet rically distributed along t he welding line,however,t he micro2hardness of TMA Z/HAZ transition zone and welding nugget zone is lower t han t hat of t he mat rix materials,which should be t he weak zone of t he welds.
K ey Words:Friction Stirring Welding,Microstructure, 7075Aluminum Alloy,Butt Welding E ffects of Different Electrolytic Ti Alloying W ays on
F atigue Crack Propagation B ehavior in Z L101A Alloy Ya ng Dec ao,Weng Y o ngga ng,Liu Wenc ai,Li Zi2 jing,Liu Zhiyo ng,Wa ng Mingxing,So ng Ti a nfu (Zhengzhou U niversity,Zhengzhou,China)2007,27 (2)148～150
Abstract The elect rolytic Al2Si2Ti alloy(AST)and t he elect rolytic low Ti aluminum base alloy(L TA)were p roduced by two met hods in t he indust rial elect rolytic tank.SE(B)specimens of ZL101A alloy obtained by above two alloys have been p repared to observe t he fa2 tigue crack propagation of t he AST alloy and L TA al2 loy.Two key parameters in t he Paris formula and crit2 ical value can be given by fitting representative data point s in one set data obtained by testing fatigue crack p ropagation rate on a M TS810material machine.The result s show t hat compared wit h ZL101A alloy p re2 pared by AST,t he ZL101A alloy prepared by L TA exhibit s better anti2fatigue crack propagation behav2 ior,which is att ributed to higher Fe content in AST alloy deteriorating t he anti2fatigue crack propagation. Therefore,eit her decreasing Fe content or modifying Fe in t he AST alloy can improve t he anti2fatigue crack p ropagation behavior of AST alloy.
K ey Words:Electrolytic Al2Si2Ti Alloy,Electrolytic Low Ti2Al B ase Alloy,Stress Concentration F actor R ange,F atigue Crack Propagation R ate,Critical V alue Mechanism of Acid Pickling for Al2Si Alloy before Spi2 ral Vibration Polishing Zha ng Ho ngya n,Li Y ua nc ai, Liu Ya ng(School of Materials Science and Engineer2 ing,Huazhong U niversity of Science and Technology, Wuhan,China)2007,27(2)151～152
Abstract It is an necessary procedure to wash t he workpiece wit h mixed acid before t he spiral vibratio n polishing,however,t he mechanism of acid pickling can not be well understood.The composition and roughness of t he surface of aluminum alloy samples before and after acid pickling were examined by X2ray p hotoelect ron spectroscopy(XPS)and contour meas2 ure apparat us.The result s show t hat major Si p hase in surface of aluminum alloy samples is dissolved by acid to form Al2O3film wit h higher roughness after acid pickling,which is cut by t he succedent spiral vibratio n polishing to form a more smoot h and bright polished surface.
K ey Words:Acid Pickling,XPS,R oughness,Al2Si Al2 loy,H2SiF6
Microstructure of R apidly2solidif ied Ti2Ni2Cu Shape Memory Alloy Ribbons He Wenjun,Min Gua nghui,Y u Hua shun(School of Materials Science and Engineer2 ing,Shandong University,Jinan,China)2007,27(2) 153～156
Abstract The micro st ruct ure of Ti51.7Ni24.5Cu23.8shape memory alloy ribbons prepared by rapid solidificatio n has been observed in t he conditions of spinning and annealing respectively.The result s show t hat micro2