镁合金/镀锌钢板电阻点焊接头拉剪断裂分析

针对2.0 mm厚的AZ31B镁合金以及1.0 mm厚的SPHC镀锌钢板,采用kDWJ-17型三相次级整流电阻焊机进行焊接试验,通过对接头的金相观察、扫描电镜分析,结合原子结合能研究点焊接头拉剪断裂特征.结果表明,点焊接头断裂的形式呈现结合面断裂和纽扣断裂两种方式,纽扣断裂抗拉剪力学性能优于结合面断裂,纽扣断裂断口是以韧性断口为主,脆性断裂为辅的混合断口.熔核区以Fe-Al化合物为主时发生纽扣断裂,熔合线边缘晶粒尺寸粗大以及熔核区Fe-Al化合物结合能大,使其断裂位置在熔合线边缘.熔核区以Mg-Zn化合物为主时发生结合面断裂,其Mg-Zn化合物结合能偏小,容易被拉断.     

AZ31B镁合金点焊接头的断口特征和耐蚀性分析

利用DN-100型固定式点焊机对AZ31B镁合金进行焊接,采用X射线衍射仪对点焊接头进行物相分析;用光学显微镜对点焊接头进行金相分析;用SEM研究点焊接头断口的微观形貌;并对焊接接头耐蚀性进行实验研究.结果表明,AZ31B镁合金母材为韧性断裂,点焊接头为脆性断裂,点焊接头的断裂倾向比母材大,耐蚀性不及母材.     

基于添加Zn中间层的汽车用镁/铝异种金属电阻点焊工艺与性能研究

采用电阻点焊并添加Zn中间层对汽车用镁合金和铝合金进行焊接,通过金相显微镜、扫描电镜和万能试验机研究了焊接接头组织和性能。结果表明,添加Zn中间层后,汽车用镁合金和铝合金电阻点焊时两侧母材分别与Zn发生反应,Zn的加入阻止了镁铝的直接接触,铝侧断口主要物相为Al、MgZn_2和Al_5Mg_(11)Zn_4,镁侧断口主要物相为Mg、MgZn_2,断裂发生在MgZn_2处。随着焊接电流或焊接时间的增加,添加Zn中间层的汽车用镁/铝异种金属焊接接头拉剪力先增加后减小,焊接电流25 kA、焊接时间500 ms、焊接压力8 kN时,接头拉剪力达到最大值4.93 kN。     

钛与低碳钢的夹铜电阻点焊接头的特性

为改善接头性能,以100 μm厚的铜箔为中间层对钛与低碳钢Q235进行电阻点焊.观察、分析了接头中各特征区域的微观结构,探讨了焊接电流、焊接时间和电极压力对接头熔核尺寸及抗剪载荷的影响.结果 表明:以铜为中间层的钛与低碳钢点焊接头熔核内部与端部分别由Ti-Fe系和Cu-Ti系金属间化合物构成.接头的抗剪载荷随焊接电流、焊接时间及电极压力的增大而呈先增大后下降的变化趋势,接头最大抗剪载荷约为4.2 kN.接头的断裂方式主要呈界面撕裂破坏,熔核内部的Ti-Fe金属间化合物呈脆性断裂,端部的Cu-Ti化合物呈准韧性断裂.     

铝箔夹层对铝-镁-硅合金车身板点焊性能的影响

采用正交试验法在两块Al-Mg-Si车身板材之间加入双层0.02 mm厚的铝箔进行点焊工艺参数试验,分析熔核微观组织的特征,研究焊接工艺参数与电阻点焊接头抗拉剪强度的关系.试验表明,焊接电流对焊点抗拉剪强度影响最大,焊接时间次之,电极压力最弱.最佳工艺参数为焊接电流17 kA、焊接时间1.0 s,电极压力2.4 kN,此时拉剪负荷为1 943 N.显微组织表明,熔核呈均匀细小的等轴晶粒,没有出现飞溅、裂纹等缺陷.接头断裂为韧性断裂,断口撕裂有韧窝特征.     

Mg/Al异种材料点焊接头显微组织研究

采用三相次级整流电阻焊机,对2mm厚AZ31B镁合金和LF6铝合金进行点焊试验,并采用扫描电镜、能谱分析、X射线衍射和显微硬度测试等方法,对Mg/Al异种材料电阻点焊接头进行了研究。结果表明,点焊熔核呈帽形,熔核组织形态以细小的等轴树枝晶为主,熔核边缘存在少量的柱状晶。Mg/Al点焊中Al原子的扩散速度远远大于Mg原子,在靠近镁侧形成了Mg17Al12金属间化合物层,其硬度高达251HV。     

6061铝合金/镀锌钢DeltaSpot电阻点焊性能分析

采用DeltaSpot带极点焊机对6061铝合金和镀锌钢薄板进行点焊,研究了焊接电流对接头组织和力学性能的影响,分析了焊接接头的断裂机理。结果表明,点焊接头的熔核直径及压痕率随电流增大先上升后趋于稳定。随着电流增大,焊接接头中金属间化合物厚度先增后减,接头的抗拉剪强度先增后降。当焊接电流为15.5kA时,接头断口形式以脆性断裂为主,塑性断裂为辅。     

基于Zn过渡层的Mg/Al点焊接头性能研究

在2 mm厚AZ31B镁合金和LF6铝合金之间添加厚度为0.1 mm的纯金属Zn进行点焊试验,通过调节焊接工艺参数来提高Mg/Al接头的性能,并确定最佳工艺参数。对Mg/Al异种材料电阻点焊接头采用拉剪试验、显微组织观察、断口扫描、能谱分析等方法进行了研究。结果表明,在接头处添加过渡层纯Zn并通过调节工艺参数能阻止金属间化合物的生成,从而使得接头的力学性能得以提升。     

电极板辅助点焊钢/铝异质接头的组织与性能

采用电极板辅助点焊进行了H220YD高强钢与6008-T66铝合金异种金属的连接,研究了接头的微观组织和力学性能.结果表明,焊接接头是通过液态铝合金在钢/铝界面处对高强钢的润湿铺展而形成的,本质上属于熔-钎焊接头.钢/铝界面上生成了由Fe2Al5和FeAl3组成的金属间化合物层.接头中铝合金熔核直径在焊接电流为14kA、焊接时间为300 ms时达最大值为9.5 mm.接头拉剪力随焊接电流的增加先迅速增大后趋于稳定,当焊接电流为12 kA、焊接时间为300 ms时达4.3 kN,比不加电极板时提高约30%.在接头拉剪过程中裂纹的扩展路径不仅沿着金属间化合物,还部分经过铝合金熔核内部.     

变形镁合金TIG焊接头组织和力学性能研究

采用TIG焊、使用与母材同质的焊丝对4.6mm厚的AZ31B变形镁合金进行焊接,利用金相显微镜、扫描电镜、显微硬度计、电子拉伸试验机等手段对焊接接头的显微组织、元素分布、断口形貌、接头硬度和强度等进行了分析.结果表明:焊缝区为细小的等轴晶,组织为α-Mg固溶体和网状分布的B-Mg17Al12金属间化合物;接头硬度分布不均匀,焊缝区最高,热影响区最低;焊缝区Mg元素烧损,Al含量较高;接头抗拉强度达到220MPa,是母材的93%,断裂发生在热影响区,断口形貌为韧-脆混合断裂.     

AZ31B镁合金电阻点焊接头断裂形式分析

以AZ31B镁合金板材为研究对象,采用基于断裂力学理论分析电阻点焊接头 拉剪力试验后的两种断裂模式,即纽扣断裂和结合面断裂.结果表明,AZ3lB镁合金焊点断裂形式受熔核边界的最大拉应力影响,当熔核边界的最大拉应力小于母材抗拉强度时,焊点发生纽扣断裂,反之则发生结合面断裂;同时,AZ31B镁合金的焊点从纽扣断裂过渡到结合...     

热冲压高强钢电阻+激光组合点焊工艺

为避免热冲压高强钢电阻点焊在热输入较大时产生飞溅和满足激光点焊装配要求,提出一种将电阻点焊和激光点焊组合的新焊接工艺方法.通过电阻+激光组合点焊工艺获得了热冲压高强钢焊接接头,分析了接头各区域的显微组织、显微硬度分布、力学性能,并分析了断裂模式及其断裂机理.结果表明,电阻+激光组合点焊接头明显分为电阻焊接区和激光焊接区.母材和激光焊核区硬度值较大,与回火区对应的软化区硬度值下降约60％,激光环外侧软化区为拉剪断裂薄弱环节.此种组合工艺获得的焊接接头相对于单独电阻点焊或激光点焊强度和韧性都有明显提高.     

Microstructure evolution and tensile properties of friction-stir-welded AM50 magnesium alloy

Friction stir welding(FSW) technique was utilized to weld cast AM50 magnesium alloy plates.The microstructures in the base metal(BM) and the weld joint were observed by optical microscopy.The mechanical properties were investigated by using hardness measurement and tensile test,and the fractographs were observed by scanning electron microscopy.The results show that the microstructure of the base material was characterized by bulk primaryαphase,α-matrix and intermetallic compoundβ(or Mg_(17)Al_(12)),and t...     

母材成分对DP590钢电阻点焊接头性能的影响

通过对两种强度相近、母材化学成分不同的DP590双相钢电阻点焊接头的强度、断口及熔核TEM分析,揭示了母材化学成分对双相钢点焊接头强韧性的影响规律及机理.结果表明,母材碳含量越高,接头正拉强度及韧性越差,其主要机理是,在电阻点焊不平衡的急速冷却条件下,随着母材碳含量的增加,在点焊熔核及熔合区形成了板条状或片状的孪晶马氏体亚结构,从而降低了接头的韧性.     

Fatigue behaviour and life estimation of Mg/Al ultrasonic spot weld bonding welds

Mg/Al dissimilar joints with favourable static and dynamic mechanical properties were obtained utilising ultrasonic spot welding and ultrasonic spot weld bonding technology. The fatigue behaviour, fatigue failure mode, and typical fatigue fracture surface morphology of Mg/Al ultrasonic spot welding and ultrasonic spot weld bonding joints were compared and observed to get a better understanding of the fatigue failure mechanism. In general, the Mg/Al ultrasonic spot weld bonding joint exhibited better fatigue performance than the ultrasonic spot welding joint. The two kinds of joints presented different fatigue failure modes with decreasing applied load level. A fatigue life prediction model was established, and the fatigue life prediction results were in good agreement with the experimental fatigue results.     

Effect of welding current on strength and microstructure in resistance spot welding of AZ31 Mg alloy

In this paper, resistance spot welding were performed on lmm-thickness magnesium AZ31B plates. The effect of welding current on the microstructure and tensile shear force was investigated. It was found that the welding current governed the nugget growth, and the nugget could not form if current levels were insufficient. The nugget revealed a homogeneous, equiaxed, fine-grained structure, which consisted of non-equilibrium microstructure of α-phase dendrites surrounded by eutectic mixtures of α and β（ Mg17All2 ） in the grain boundaries. With increasing welding current, the size of grains in nugget would be more smaller and uniform, and the width of plastic rings would be larger. Tensile shear tests showed that tensile shear force of the joints increased with increasing welding current when the welding current was smaller than 17 000 A. The maximum tensile shear force was up to 1980 N.     

Fatigue behaviour of Al/steel dissimilar resistance spot welds fabricated using Al–Mg interlayer

Aluminium alloy sheets were joined to stainless steel ones by a resistance spot welding method using Al–Mg alloy interlayer. The interlayer exhibits a lower melting point than the Al alloy. Consequently, melted interlayer with a lower temperature filled the gap between the two sheets and resulted in effective joining. Subsequently, tensile shear fatigue tests had been conducted to evaluate fatigue strength and to determine the fatigue fracture mechanism. Resistance spot welding dissimilar welds exhibited higher fatigue strengths than friction stir spot welded dissimilar ones. Fatigue fracture modes were dependent on the load levels, where plug type fracture occurred at high load levels, shear fracture through the nugget at medium load levels and through thickness fatigue crack propagation in the Al sheet at low load levels. The fracture mode transition was attributed to the geometrical rotation around the nugget.     

Optimization of parameters and study of joint microstructure of resistance spot welding of magnesium alloy

Experimental investigations on the DC spot welding of Mg alloy AZ31B are presented. Experiments are carried out to study the influence of spot welding parameters （ electrode force, welding heat input and welding time） on the tensile shear load and the diameter of nugget, based on an orthogonal test and analysis method. The optimum parameters are as follows： electrode force is 2 000 N, welding heat input is 80% and welding time is 6 cycles. The microstrueture of spot weld is single fine equiaxed crystals in the nugget, of which the structure is β-Mg17Al12 precipitated on α-Mg boundaries induced by nonequilibrium freezing. And the surface condition of the workpiece has great influence on the joint quality.     

Mechanical properties and interface morphology of Mg/Al ultrasonic spot weld bonding welds

This paper investigates the mechanical properties and interface morphology of Mg/Al ultrasonic spot welding (USW) joint, adhesive bonding (AB) joint and ultrasonic spot weld bonding (USWB) joint. The peak load and fracture energy of USWB joint increased significantly compared to that of USW joint and AB joint. The USWB joint presented a hybrid fracture mode which was composed of the delamination failure at adhesive/Mg interface, cohesive failure within the adhesive and cleavage failure in the weld zone. The interface morphology suggested that USWB joint exhibited fewer defects in the cured adhesive matrix and elevated connection density of adhesive/metal interface, which improved joint strength and altered the fracture mode.     

双相钢点焊熔核界面撕裂失效模式参数控制

采用改进响应面试验分析方法对影响1.4 mm双相钢DP600点焊接头界面撕裂失效模式的工艺参数进行研究.结果表明,焊接电流、焊接时间以及保持压力是影响双相钢焊点界面撕裂失效模式的关键参数,合适的焊接工艺参数有助于提升熔核直径比,并且降低其对焊接参数的敏感度.以焊接工艺的鲁棒性为优化目标,获得了控制焊点界面撕裂失效模式的...