厚板铝合金搅拌摩擦焊接头的冲击性能

采用搅拌摩擦焊对厚度为30 mm的2A12铝合金板材进行对焊连接,分析了接头不同厚度处的微观组织与冲击性能。结果表明:随着热输入量的减少,接头上层的晶粒相比于下层出现了粗化现象,导致接头上层区域的冲击韧性低于下层。焊核区晶粒最为细小,热机影响区次之,热影响区晶粒最为粗大;焊核区的冲击韧性高于热影响区,热机影响区由于存在微型裂纹,所以冲击韧性最低。焊核区上层的晶粒尺寸小于热机影响区下层的晶粒尺寸,但焊核区上层的冲击韧性低于热机影响区下层的冲击韧性,这是由于焊核区所含的Al₂CuMg脆性第二相的数量较多。焊接接头冲击韧性的变化不仅与焊缝不同区域的微观组织变化有关,还与该区域的第二相数量有关。     

6082-T6铝合金搅拌摩擦焊接头的显微组织与力学性能

对8mm厚的6082-T6铝合金进行了搅拌摩擦焊接试验,焊后对工艺参数与接头显微组织及力学性能的关系进行了分析。结果表明：焊核区显微组织为细小等轴晶组织。分析焊接速度对接头抗拉强度的影响得出规律：随着焊接速度的增大,接头强度增大,但焊接速度达到一定值时,接头性能达到最高值,之后随着焊接速度变大,接头就会出现缺陷,影响接头的性能。     

7050-T7451铝合金搅拌摩擦焊接头组织和性能

在不同焊接工艺参数下对3.5 mm厚的7050-T7451铝合金进行了搅拌摩擦对接焊,并对焊缝成形质量、接头微观组织演变和拉伸性能进行了深入研究。结果表明,当搅拌头旋转速度(ω)在400～1 000 r/min、焊接速度(v)在50～300 mm/min时,均可获得内部无缺陷的接头。当焊接速度不变时,随搅拌头旋转速度的增加,接头的拉伸性能先增大后减小。当搅拌头旋转速度为600 r/min、焊接速度为150 mm/min时,接头的拉伸性能最好,抗拉强度为475 MPa,强度系数达90%,伸长率为5.7%。当ω/v的值处于4～6之间时,可获得拉伸性能优良的接头。     

铝合金搅拌摩擦焊接头微观组织和力学性能分析

目的 研究7020铝合金搅拌摩擦焊(FSW)的结构和机械性能。方法 采用搅拌摩擦焊对铝板进行对接焊试验,具体形式为单面焊双面成型。采用拉伸机和显微维氏硬度仪对试样进行力学性能测试;利用蔡司金相、光谱仪、扫描电子显微镜、X射线衍射仪研究母材和焊接接头的微观组织。结果 在硬度上,母材>热影响区>焊核区,热影响区平均硬度约为94HV,母材平均硬度为99HV,焊核区平均硬度最低为78HV,焊核区出现“S”缺陷,在一定程度上弱化了焊核区性能;7020铝合金搅拌摩擦焊接头的抗拉强度为235 MPa,屈服强度为158 MPa,屈强比为0.67,伸长率为7%,焊接系数可以达到73.8%;母材的抗拉强度为325 MPa,屈服强度为278 MPa,屈强比为0.86,伸长率为25%;焊接接头中心显微组织主要由胞状树枝晶体组成,显微结晶依次呈现为平面晶、胞状晶、树枝状晶、等轴晶;铝合金母材和焊接接头的金属相组成均为α?Al+Mg2Si;焊接接头断口呈现比较明显的韧性断裂特征。结论 铝合金搅拌摩擦焊可以获得性能比较优良的焊接接头,为其他铝合金材料的FSW焊接提供技术参考。     

铝合金搅拌摩擦对接焊接头组织与性能研究

研究了5083铝合金搅拌摩擦焊(FSW)焊接接头组织与性能,采用金相显微镜观察焊接接头各区域的微观组织,并对接头显微硬度和力学性能进行了测定。结果表明,5083铝合金搅拌摩擦焊焊核组织为动态再结晶生成的细小组织,强化相均匀分布;热机影响区由于动态再结晶和焊接热循环的双重作用,组织变化较大,晶粒有一定程度的长大,强化相有所细化;热影响区仅仅受到热循环作用,使得晶粒粗化和强化相出现聚集现象。搅拌摩擦焊接接头中心硬度与母材基本相当,热机影响区和热影响区由于焊接热输入的原因,使得硬度有所降低。搅拌摩擦焊室温拉伸性能和冲击性能不低于母材的,其中拉伸试样均断裂于母材,焊核室温冲击值达到母材的1.5倍以上,热影响区冲击值与母材的相当。     

静轴肩搅拌摩擦焊2A14-T4铝合金T形接头的组织和性能

采用静轴肩搅拌摩擦焊技术实现了8.5 mm厚2A14-T4铝合金T形接头的焊接,研究了接头的宏观成型、显微组织及力学性能.结果表明:焊缝表面呈现光滑无弧纹特征,焊缝外部和内部未发现焊接缺陷;SSFSW T形接头截面焊接区域形貌整体呈现两头宽、中间窄的"开口哑铃"状,焊核区晶粒表现为取向随机的等轴晶,焊核区平均晶粒尺寸表现为第二次焊核区最大,焊接重合区次之,第一次焊核区最小.焊核区再结晶机制以几何动态再结晶为主并伴随有部分连续动态再结晶;热机影响区较窄且晶粒被拉长变形,热影响区组织晶粒长大粗化;焊接过程中第二相粒子的析出粗化造成焊核区硬度降低,硬度最低点出现在第一道焊缝热影响区与热机影响区的交界处;接头的硬度较低区域和结构尺寸引起的应力集中导致T形接头底板与筋板容易萌生裂纹、发生断裂;断口中存在较多的撕裂棱以及大小不一的韧窝,在韧窝中存在尺寸不均匀的第二相颗粒,断口呈现韧性断裂特征.     

5083铝合金搅拌摩擦焊接头的显微组织与力学性能

对8 mm厚5083-H321铝合金板进行了搅拌摩擦焊接试验,研究了焊接工艺参数对搅拌摩擦焊接头显微组织和力学性能的影响。结果表明:该搅拌摩擦焊接头焊核区显微组织为细小的等轴晶组织,热机影响区为拉伸弯曲变形组织,热影响区非常窄,其晶粒尺寸与母材相当;综合接头表面形貌和拉伸性能得到较佳的搅拌摩擦焊接工艺参数为使用搅拌针为三棱形带螺纹、轴肩为内扣型的搅拌头,主轴转速为300 r·min^-1,焊接速率为120 mm·min^-1;在该工艺条件下接头表面成形良好,抗拉强度可达到母材的94.5%。     

超声冲击对铝合金搅拌摩擦焊接头组织及性能的影响

目的分析超声冲击对铝合金搅拌摩擦焊成形后接头的组织及耐蚀性的作用效果。方法采用超声冲击设备对2A12铝合金搅拌摩擦焊接头表面进行超声冲击处理,并对超声冲击前后接头的显微组织、显微硬度以及耐腐蚀性能进行了分析。结果经过超声冲击处理后的铝合金接头上表面会产生一层塑性变形层,并且塑性层内位错密度增大,使表层金属得到一定程度的加工硬化,促使冲击后接头各区域的表面硬度明显提高,冲击后接头热机械影响区和热影响区硬度提高达60%以上;腐蚀浸泡试验发现,超声冲击后接头的点腐蚀程度较超声冲击前明显减缓,腐蚀速率约是冲击前的1/2。结论超声冲击有效改善了铝合金搅拌摩擦焊接头区域材料过时效的软化现象,并且有效改善了接头的抗腐蚀性能。     

厚板7022铝合金搅拌摩擦焊接实验研究

对10mm厚度的7022铝合金进行了搅拌摩擦焊接,获得表面光滑的焊接接头,并通过X射线检测焊缝无裂纹和气孔。研究该搅拌摩擦焊接头不同区域的显微组织特征,并通过拉伸、冲击和硬度试验分析了焊接接头的力学性能。结果表明,焊缝处组织为细小均匀的等轴晶粒;在搅拌头转速为400r/min,焊接速度为100mm/min时焊接接头的抗拉强度、屈服强度均比母材高;焊接接头的冲击韧性比母材高;焊接接头显微硬度比母材稍低,焊接接头具有良好的力学性能。     

焊后时效处理对6082-T6铝合金搅拌摩擦焊接头的影响

对6082-T6铝合金搅拌摩擦焊接头进行自然时效和人工时效处理,通过透射电子显微镜、扫描电子显微镜、拉伸实验机和显微硬度计对组织演变和力学性能进行研究。结果表明:人工时效处理后显微硬度比焊态和自然时效高10~25HV,提高焊核区和热机影响区硬度效果明显好于自然时效。经过焊后自然时效、人工时效的焊接接头力学性能得到一定程度的提升,人工时效析出相比自然时效析出相抗拉强度提高12%,延伸率降低9%,人工时效提高拉伸强度效果更明显。人工时效处理后,焊核区组织发生显著变化,NZ主要为GP区,经过人工时效后NZ强化效应随团簇和GP区尺寸增大及数量增多而加强。HAZ主要为粗大的β′,经过人工时效后变化不大,硬度基本保持不变。通过对微观组织进行研究发现析出物的形状由界面能和应变能决定。     

Microstructure evolution and mechanical properties of friction stir welded FeCrNiCoMn high-entropy alloy

To investigate the microstructural development and mechanical properties of friction stir welded high-entropy alloy, the stirring process and the air cooling period were separated for discussion. The texture component developed from A* {111}<112> to A {111}<110> in the stirring stage, and finally changed to B {112}<110> in the subsequent air cooling stage caused by the multiple mechanisms including discontinuous dynamic recrystallization, continuous dynamic recrystallization, static recovery and selected grain growth. This work also demonstrated that the static recovery and the selected grain growth during the air cooling stage remarkably deteriorated the microstructure and mechanical properties which is produced during the stirring stage, and it cannot be neglected when investigating the microstructure transformation and mechanical properties during the friction stir welding.     

Formation and mechanical properties of stationary shoulder friction stir welded 6005A-T6 aluminum alloy

6005A-T6 aluminum alloy is welded by stationary shoulder friction stir welding (SSFSW). At a constant rotational velocity of 2000 rpm, the effect of welding speed on mechanical properties of SSFSW joint are investigated in detail. Defect-free joint with gloss surface and small flash is attained and no cracks appear at the bending angle of 180°. Compared with traditional friction stir welding (FSW), width of rotational shoulder affected zone is relatively small because of the smaller diameter of rotational shoulder. Increasing welding speed is benefit for reducing the width of softening region and the softening degree. The fracture position of welding joint locates in thermo-mechanically affected zone and the fracture surface morphology presents the typical ductile fracture. The maximum tensile strength of joint at the welding speed of 400 mm/min reaches 82% of base metal (BM).     

铝/镀锌钢搅拌摩擦铆焊接头组织与力学性能

为实现铝钢之间的优质连接,采用搅拌摩擦铆焊新方法对6061铝合金和DP600镀锌钢进行搭接点焊,利用扫描电子显微镜、能谱仪及拉伸试验对接头的微观组织及力学性能进行了研究.结果表明:接头成形平整美观,中心没有匙孔;接头包含铆接区和扩散区,其中在铆接区铝合金以铝柱的形式嵌入到钢板的圆孔中,形成了一个"铝铆钉",底部有富铝的α固溶体偏聚,圆孔四周形成扩散区,铝和钢形成了冶金结合,依靠金属间化合物Fe Al3连接在一起;接头有3种断裂形式,在最佳工艺参数下接头的抗剪力达到8.2 k N;铝柱上断口的微观形貌是被拉长的韧窝,扩散区的断口由灰色基体和白色颗粒组成.     

几何参数对2219铝合金拉拔式摩擦塞补焊接头微观组织及力学性能的影响EI北大核心CSCD

拉拔式摩擦塞补焊是火箭贮箱制造过程的重要技术之一。研究8 mm厚2219-T87铝合金拉拔式摩擦塞补焊接头的几何形状及其对接头微观组织和力学性能的影响。结果表明:塞孔及成形环几何形状对接头界面结合质量有重要影响。当焊接工艺参数为7000 r·min^(-1)主轴转速,35 kN轴向拉力以及16 mm轴向进给量时,使用锥直孔塞孔可有效防止塞棒在焊接过程中发生颈缩,从而消除接头未焊合缺陷;使用阶梯孔形成形环可以改善接头界面受力状态,防止弱结合缺陷产生。微观组织分析表明,毗邻结合界面的母材侧组织发生动态再结晶,热机械影响区组织发生明显塑性变形。接头附近组织受焊接热循环和塞棒旋转挤压作用发生明显软化,硬度最低值出现在热机械影响区,约为90HV。当接头存在焊接缺陷时,接头抗拉强度及伸长率较母材大幅降低,而无缺陷焊接接头的抗拉强度及伸长率分别为360.1 MPa和6.45%,接头系数为0.828,断裂方式为韧性断裂。     

Improving mechanical properties of pinless friction stir spot welded joints by eliminating hook defect

Hook defect (HD) seriously decreases the mechanical properties of friction stir spot welded (FSSW) joints. In this study, two methods were therefore used to eliminate the HD in pinless FSSW joints. The one is changing welding parameters such as rotating speed and dwell time. The other one is FSSW plus subsequent friction stir welding (FSSW-FSW), which is an innovative method proposed in this study. Experimental results showed that the HD in pinless FSSWed AA2024 joints was successfully eliminated by using FSSW-FSW, not by changing process parameters. The joints without HD exhibited a tensile–shear load of as much as 12 kN, which was higher than that of 6.9 kN in the joints with HD. Furthermore, it was proved that the tensile–shear load is not greatly improved only by increasing the nugget zone when HD still existed in the FSSW joints. In addition, the fracture morphology analysis demonstrated that the shear fracture of the FSSW-FSW joints took place along the boundary between the upper and lower sheets through the weld nugget, and the faying surface between the two sheets was completely sheared off.     

Effect of friction stir welding on the microstructure and mechanical properties of AA 6063-T6 aluminum alloy

In this study, AA 6063-T6 alloy plates were joined via friction stir welding using three different pin geometries (i. e., helical threaded, pentagonal and triangular) under various process parameters of tool rotational speed and welding speed. The microstructures and mechanical properties of the various welded joints were investigated. Macro-structural observations revealed that kissing bonds occurred in the welded joints due to fractured oxide layers. X-ray diffraction analysis indicated that the stir zones of the welded joints exhibited phases of Al₈Fe₂Si, Al₅FeSi, and Mg₂Si. In the welded joints, processed using a helical threaded pin, no tunnel-type defect was detected to occur; specimens were fractured outside of the joint region during tensile tests, indicating that the kissing bonds formed in the stir zones did not cause any deterioration in tensile strength or ductility. The welded joints processed using a helical threaded, pentagonal and triangular pin at 500 min⁻¹ tool rotational speed and 80 mm min⁻¹ welding speed exhibited a ductile deformation behavior along with a tensile strength in the range of 153 MPa to 155 MPa.     

Microstructure and fatigue performance of friction stir welded joints of 2A12-T4 and 7075-T6 dissimilar aluminum alloy

The objective of this work is to investigate the microstructure and fatigue performance of friction stir welding joint of 2A12-T4 and 7075-T6 dissimilar aluminum alloy. Microstructure shows that the grain growth of heat-affected zone in both sides of joint is noticeable; the grain size of thermo-mechanically affected zone in both sides of joint is deformed and distorted in various degrees; nugget zone is fine equiaxed grain with uniform distribution. Microhardness of joint presents an approximate “W” types distribution on the whole, and the highest hardness value of the joint appears near the center of nugget zone, up to 146.5 HV0.2. Since the joint has the higher the fatigue strength ratio, and the S−N curve of the joint shows a smaller downward trend, the joint has the best fatigue performance and 7075-T6 base metal has the worst fatigue performance. Linear fitting of 7075-T6 base metal is ; linear fitting of 2A12-T4 base metal is ; linear fitting of joint is . The fracture analysis presents that the low-cycle fatigue fracture mechanism of welding joint is quasi-cleavage fracture, and the main mode of high cycle fatigue fracture is the inter crystalline fracture, mixed with ductile fracture.     

电磁铸造5182铝合金锭的组织与性能研究

采用电磁铸造技术铸造了易拉罐用5182变形铝合金，采用光学显微镜和扫描电镜分析了其显微组织，而且对其进行了均匀化处理和对比实验。结果表明，电磁铸造锭有更加良好的内部组织和优良的力学性能，电磁铸造试样的硬度大约是普通连续铸造试样的两倍，疲劳性能是普通连续铸造铸锭的3倍，电磁铸造铸锭还有良好的耐磨性，电磁铸造锭的优良性能得宜于电磁搅拌的作用使整个铸锭获得均匀细小的晶粒组织，电磁铸造技术是一种无模铸造技术，它依靠电磁力约束液体金属成型，液体金属不与铸模接触，铸锭表面光滑如镜；相反，普通连续铸造锭表面因存在振动痕和亚表面偏析等铸造缺陷，力学性能大大降低。     

Microstructure and mechanical properties as a function of rotation speed in underwater friction stir welded aluminum alloy joints

A 2219-T6 aluminum alloy was underwater friction stir welded at a fixed welding speed and various rotation speeds in order to illuminate the influence of rotation speed on the performance of underwater joints. With increasing rotation speed, the hardness of the stir zone (SZ) gradually increases due to the increase in dislocation density. The tensile strength first increases from 600 to 800 rpm and then reaches a plateau in a wide rotation speed range. After that a remarkable decrease in tensile strength occurs owing to the formation of void defect. The joint welded at lower rotation speed tends to be fractured in the SZ. At higher rotation speeds, the hardness increase in the SZ makes the fracture locations of defect-free joints move to the thermal-mechanically affected zone (TMAZ) or heat affected zone (HAZ).     

Nanomechanical properties of friction stir welded AA6082-T6 aluminum alloy

Lightweight alloys are of major concern, due to their functionality and applications in transport and industry applications. Friction stir welding (FSW) is a solid-state welding process for joining aluminum and other metallic alloys and has been employed in aerospace, rail, automotive and marine industries. Compared to the conventional welding techniques, FSW produces joints which do not exhibit defects caused by melting. The objective of the present study is to investigate the surface hardness (H) and elastic modulus (E) in friction stir welded aluminum alloy AA6082-T6. The findings of the present study reveal that the welding process softens the material, since the weld nugget is the region where the most deformations are recorded (dynamic recrystallization, production of an extremely fine, equiaxial structure), confirmed by optical microscopy and reduced nanomechanical properties in the welding zone. A yield-type pop-in occurs upon low loading and represents the start of phase transformation, which is monitored through a gradual slope change of the load-displacement curve. Significant pile-up is recorded during nanoindentation of the alloy through SPM imaging.