Interface morphology and microstructure of high-power ultrasonic spot welded Mg/Al dissimilar joint

High-power ultrasonic welding technology, which has the excellent characteristics of low-energy input and high efficiency, can effectively shorten the welding time, reduce the formation of intermetallic compounds (IMCs), and improve the strength of Mg/Al dissimilar welded joints in the future manufacturing industry. Mg/Al dissimilar metal ultrasonic welded joints with favourable mechanical properties were obtained through reasonable selection of sonotrode patterns and optimisation of welding parameters. The connection mechanisms of joints were discussed based on the analysis of weld interface morphology, microstructure evolution, and the composition and distribution of Mg–Al IMCs that varied with welding energy. The mechanical interlocking phenomenon and discontinuously distributed Mg₁₇Al₁₂ with low thickness were observed at the weld interface, which helped to improve the joint performance.     

Effect of lattice matching degree and intermetallic compound on the properties of Mg/Al dissimilar material welded joints

The welding of Mg/Al dissimilar materials with different filler metal was investigated, and the quantities and kinds of intermetallic compounds were discussed. In addition, the matching degrees between base metal and intermetallic compounds were defined and calculated, and the effect of different quantities of each intermetallic compound on the property of welded seam was investigated. The results indicated that the welded seam was composed of Al₃Mg₂ and Al₁₂Mg₁₇ by Mg/Al directly gas tungsten arc butt welding, and only one intermetallic compound of MgZn₂ formed in the welding seam using Zn and Zn–xAl filler metal. The tensile strengths of the joints increased with the increase of the matching degrees between the intermetallic compounds and the base metal when the welded seam contained different intermetallic compound. Meanwhile, the tensile strengths of the joints are decreased with the increase of intermetallic compound content when the welded seams contained the seam intermetallic compound.     

Reducing Intermetallic Compounds of Mg/Al Joint in Friction Stir Lap Welding

To reduce intermetallic compounds (IMCs) of Al₁₂Mg₁₇ and Al₃Mg₂ in Mg/Al friction stir lap welding joint, pin tip was plunged into the lower sheet at a small distance. Results showed that at a fixed welding speed of 50 mm/min, sound joints were obtained using rotating speeds from 750 to 500 rpm, and the IMCs zones were rather small. Cracks easily appeared inside IMCs inside onion ring and at lap interface. Therefore, reducing the IMC was beneficial for reducing the crack. Joint lap shear stress firstly increased and then decreased with decrease in the rotating speed. The maximum shear stress of 50.2 MPa was attained at a rotating speed of 500 rpm because of reduced IMC.     

Microstructure and mechanical properties of friction stir lap welded Mg/Al joint assisted by stationary shoulder

Using magnesium alloy as upper sheet, 3 mm-thick AZ31 magnesium alloy and 6061 aluminum alloy were joined using friction stir lap welding assisted by stationary shoulder. The effects of tool rotating speed on cross-sections, microstructure and mechanical properties of Mg/Al lap joints were mainly discussed. Results showed that stationary shoulder contributed to joint formation, by which stir zones (SZ) were characterized by big onion rings after welding. Because of the big forging force exerted by stationary shoulder, the upper region of hook was well bonded. SZ showed much higher hardness because of intermetallic compounds (IMCs). The bonding conditions at the base material (BM)/SZ interface at advancing side and the hook region played important roles on joint lap shear properties. The X-ray diffraction pattern analysis revealed that the main IMCs were Al₃Mg₂ and Al₁₂Mg₁₇.     

The constitutional liquation at the interface of Al/Mg friction welding joints

Constitutional liquation occurred at the friction interface of Al/Mg joints produced by continuous drive friction welding. This paper investigated the relationship between constitutional liquation and microstructure morphology of Al/Mg joints. The intermetallic compound γ-Al₁₂Mg₁₇ underwent morphological transitions from submicron-size particles to island-like lamellae, then to network structure as the Al content increased. The submicron-size γ-Al₁₂Mg₁₇ particles precipitated along the grain boundaries of α-Mg solid solution. The Mg–Al₁₂Mg₁₇ divorced eutectic structure was formed. The formation mechanism of eutectic structure was studied with Al–Mg binary phase diagram and Al–Mg–Zn ternary phase diagram. The network structure was derived from dendritic structure γ-Al₁₂Mg₁₇. Friction pressure could improve the liquid–solid hybrid microstructure morphology at the welding interface.     

Microstructure and mechanical behaviour of cold metal transfer welded Mg/Al dissimilar joint using wire AZ31 as filler metal

Mg/Al dissimilar butt joint was produced by modified cold metal transfer process using wire AZ31 as filler metal. The energy input characteristics and the microstructure and mechanical behaviour of the joint were investigated. Microstructural analysis shows that a diffusion Mg–Al intermetallic compounds interface layer formed along the weld boundary near Al substrate. The interface layer consisted of three intermediate layers from Al substrate to weld metal: Mg₂Al₃ layer, Mg₁₇Al₁₂ layer and Mg₁₇Al₁₂?+?α-Mg solid solution eutectic layer. The tensile strength of the welded joint was 38.4?MPa, which was fairly dependent on the lowest strength of the three intermediate layers. The brittle fracture occurred primarily within the thinnest Mg₂Al₃ intermediate layer adjacent to Al substrate.     

Fabrication and performance evaluation of dissimilar magnesium–aluminium alloy multi-seam friction stir clad joints

This investigation is aimed to establish empirical relationships between continuous multi-seam friction stir cladding process parameters (i.e., rotational speed, welding speed and shoulder overlap ratio) and the quality characteristics (bond tensile strength, shear strength and corrosion) of dissimilar magnesium–aluminium alloy clad joints. The influence of considered process parameters on the clad properties was reported. Furthermore, multi-criterion optimization procedure was used to obtain ideal processing conditions, which can yield higher interface strength and lower corrosion rate of fabricated composite plate. Results indicate that, the aluminium-rich thin continuous layer, Mg-rich irregular shaped regions consists of Al₃Mg₂ and Al₁₂Mg₁₇ intermetallic compounds and nature of mechanical interlocking has great influence on the joint interface strength. On the other hand, the corrosion resistance of the clad joints is greatly affected by the amount of magnesium mixed with top aluminium sheet during friction stirring. Also, bend testing shows that, the cladded joints exhibit excellent ductility.     

Properties of as welded and heat treated pure titanium–7075 Al–Zn–Mg alloy friction weld joints

Abstract

The effects of joining conditions and an age hardening post­weld heat treatment (PWHT) at 120°C for 24 h on the tensile strength and metallurgical properties of dissimilar friction joints between pure titanium and age strengthened 7075 Al–Zn–Mg alloy were investigated. Highest strength was achieved using intermediate friction pressure (150 MPa), short friction time (0.5 s), and high upsetting (forging) pressure (400 MPa). The joint tensile strength decreased when the joint diameter was increased from 8 to 16 mm. The joint tensile strength of as welded (AW) dissimilar joints was similar to that of PWHT joints with diameters of 8, 12, and 16 mm. Detailed TEM confirmed that there was a negligible difference in the thickness of the intermetallic layer formed at the dissimilar joint interface for AW and PWHT joints. While the intermetallic phases formed at the joint interface comprised Al₃Ti, τ (Ti₂Mg₃Al₁₈), and Al in AW joints, they consisted of Al+τ or Mg₂Al₃+τ+Al in PWHT joints. Softened regions were generated in 7075 base material immediately next to the interface in AW joints. Post­weld heat treatment increased the hardness of the softened region almost to that of as received 7075–T6 base material in 12 and 16 mm diameter joints. In contrast, the hardness of the softened region in 8 mm diameter joints could not be recovered to that of the as received material. This was a result of overaging and coarse precipitates in the softened region produced during the friction welding operation.     

Study on TIG welding of dissimilar Mg alloy and Cu with Fe as interlayer

Abstract

Dissimilar Mg alloy and Cu lap joints were prepared by tungsten inert gas (TIG) welding with Fe as an interlayer, without producing intermetallic compounds MgCu₂ and Mg₂Cu. Copper and Fe were joined together in the form of remelt deposit welding and Mg alloy and Fe plate were joined together in the form of brazing. During tensile testing, the joints between Fe plate and Mg alloy fractured, and Mg alloy and Fe plate were joined together by interatomic force. Metallic oxides produced in the interface between Mg and Fe resulted in reduction in the mechanical properties of the welded joints.     

Materials flow and phase transformation in friction stir welding of Al 6013/Mg

Material flow and phase transformation were studied at the interface of dissimilar joint between Al 6013 and Mg, produced by stir friction welding (FSW) experiments. Defect-free weld was obtained when aluminum and magnesium were placed in the advancing side and retreating side respectively and the tool was placed 1 mm off the weld centerline into the aluminum side. In order to understand the material flow during FSW, steel shots were implanted as indexes into the welding path. After welding, using X-ray images, secondary positions of the steel shots were evaluated. It was revealed that steel shots implanted in advancing side were penetrated from the advancing side into the retreating side, whereas the shots implanted in the retreating side remained in the retreating side, without penetrating into the advancing side. The welded specimens were also heat treated. The effects of heat treatment on the mechanical properties of the welds and the formation of new intermetallic layers were investigated. Two intermetallic compounds, Al₃Mg₂ and Al₁₂Mg₁₇, were formed sequentially at Al6013/Mg interface.     

Electron beam welding of SiCp/2024 and 2219 aluminum alloy

SiC_p/2024 matrix composites reinforced with SiC particles and 2219 aluminum alloy were joined via centered electron beam welding and deflection beam welding, respectively, and the microstructures and mechanical properties of these joints were investigated. The results revealed that SiC particle segregation was more likely during centered electron beam welding (than during deflection beam welding), and strong interface reactions led to the formation of many Al₄C₃ brittle intermetallic compounds. Moreover, the tensile strength of the joints was 104 MPa. The interface reaction was restrained via deflection electron beam welding, and only a few Al₄C₃ intermetallic compounds formed at the top of the joint and heat affected zone of SiC_p/Al. Quasi-cleavage fracture occurred at the interface reaction layer of the base metal. Both methods yielded a hardness transition zone near the SiC_p/2024 fusion zone,and the brittle intermetallic Al₄C₃compounds formed in this zone resulted in high hardness.     

SiC_p/2024与2219铝合金电子束焊接

分别采用电子束对中焊、偏束焊技术,研究了Si C颗粒增强铝基复合材料Si Cp/2024与2219铝合金的接头组织及力学性能.结果表明,对中焊时接头易出现Si C增强相的偏聚,同时发生严重的界面反应,生成大量脆性相Al4C3,接头抗拉强度最高为104 MPa.采用偏束焊工艺可以很好地抑制界面反应,通常只在焊缝上部与Si Cp/Al热影响区上部生成少量脆性相Al4C3,接头抗拉强度最高可达131 MPa.试件均断裂在母材界面反应层上,且为明显的脆性断裂.不同工艺下接头横截面硬度分布存在突变区,该区域在Si Cp/2024熔合区附近,该处脆性相Al4C3的生成导致硬度升高.     

AZ31B镁合金/镀锌钢板电阻点焊接头形成机理

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,通过光学金相、扫描电镜等方法分析接头各区域的组织结构和成分分布.提出了镁锌低熔点化合物挤压机制,分析了Zn元素在镁合金和镀锌钢板电阻点焊中的作用.结果表明,Zn与Mg元素形成的低熔点化合物MgZn₂在电极压力的作用下能填满由于焊接变形引起的间隙,使反应界面密封,促进Fe,Al元素在界面发生处扩散,Fe与Al元素在界面处发生反应生成Fe₂Al₅化合物,从而形成高强度的镁合金与镀锌钢板的电阻点焊接头.     

铜对钢/铝激光-MIG复合焊接头组织及性能的影响

采用激光-MIG复合焊方法研究了铜对SYG960E超高强度度钢/6061铝合金焊接接头微观组织及力学性能的影响.结果表明,与MIG焊相比,激光-MIG复合焊有利于改善焊缝成形及焊接质量.钢/铝界面层具有双层结构,靠近铝焊缝侧为针状的FeAl₃金属间化合物,而靠近钢母材侧为条状的Fe₂Al₅金属间化合物.铜对钢/铝界面层及接头的力学性能具有显著的影响.添加铜后可以有效地减小界面层厚度和裂纹敏感性,降低钢/铝接头的最高硬度,明显提高接头的抗拉强度,接头强度可以提高110%,这主要与铜抑制界面层生长和改善界面层中Fe-Al金属化合物的脆硬性有关.     

镁与镀锌钢板脉冲旁路耦合电弧熔钎焊

采用脉冲旁路耦合电弧熔钎焊,使用AZ92A镁合金焊丝在镀锌钢板上进行平板堆焊试验,通过调整焊接工艺参数,能在最佳的焊接参数下得到熔宽均匀,成形良好的焊缝.通过SEM,EDS,EPMA等测试手段对焊接接头界面中心区的微观组织进行观察与分析,及对焊缝的剥落面进行XRD测试发现有Mg₁₇Al₁₂,Mg_0.97Zn_0.03和Fe₄Zn₉金属间化合物形成.结果表明,在适当参数下,利用脉冲旁路耦合电弧熔钎焊可获得镁与镀锌钢板的焊缝,且镁与镀锌钢板异种金属电弧熔钎焊时镁和铁都与锌反应形成了金属间化合物.     

Influence of alloy elements on microstructure and mechanical property of aluminum–steel lap joint made by gas metal arc welding

5052 aluminum alloy sheets and galvanized mild steel sheets were joined in lap configuration by alternate-current double pulse gas metal arc welding with pure Al, Al–5Si, Al–12Si and Al–4.5Mg (wt%) filler wires. The effect of alloying elements on the microstructure of intermetallic compounds (IMC) layers formed between weld seam and steel, and tensile strength of the resultant joints were investigated. The thickness of IMC layer in all samples varied along the cross-section of the joint, the intermediate part of the IMC layer was thicker than the head and root parts. The diffusion of Si into Fe₂Al₅ sub-layer could restrain the growth of Fe₂Al₅ sub-layer and IMC layer, and joint's mechanical property improved with the increasing Si content in Fe₂Al₅ phase. Due to the high hot crack sensitivity of Al–4.5Mg alloy, cracks generated at the root of joint made with Al–4.5Mg filler, resulting in poor mechanical property.     

Microstructural modification and mechanical property improvement in friction stir zone of thixo-molded AE42 Mg alloy

Thixo-molded AE42 Mg alloy was friction stir welded, and the soundness of joints was evaluated, together with the microstructure evolution and mechanical properties in friction stir zones. According to X-ray radiography, the optimum FSW condition range of AE42 alloy exists between AZ61 and AZ31 alloys, and it seems that the optimum welding condition range increases with decreasing Al content in the Mg alloys. There are mainly two kinds of compounds in the thixo-molded AE42 alloy, and FSW has little influence on the grainy Al₁₀RE₂Mn₇ compound, but it has great influence on Al₁₁RE₃ phase, which is changed from lamellar eutectic to small particles after welding. Furthermore, the average diameter of Al₁₁RE₃ particles in SZ decreases with increasing the traveling speed at constant rotation speed due to less heat input. The hardness in SZ is higher than that in BM, and tensile strength and elongation are both improved after welding because the stirring refines and uniforms the microstructure and intermetallic compounds.     

Effect of Melt-to-Solid Insert Volume Ratio on Mg/Al Dissimilar Metals Bonding

Compound casting is used as a process to join various similar and dissimilar metallic couples. The ratio of melt-to-solid volume is one of the main factors that can affect the contact time between melt and the solid insert. In this investigation, magnesium and aluminum metals (magnesium as the cast metal and aluminum as the solid insert) having melt-to-solid volume ratios (V _m/V _s) of 1.25, 3, and 5.25 were successfully bonded via compound casting. Results demonstrated that by increasing the ratio of V _m/V _s from 1.25 to 5.25, the thickness of the reaction interface between Al and Mg varies within the range of 200 to 1800 μm. X-ray diffraction, scanning electron microscopy, and Vickers microhardness study of the bonding of these two metals showed that the interface consisted of three separate sub-layers within reaction layer. These sub-layers had higher hardness than those of the Al and Mg bulk metals. In all specimens, composition of the sub-layer adjacent to Al (layer I) was Al₃Mg₂ and that adjacent to Mg (layer III) was Al₁₂Mg₁₇/(Mg) eutectic structure. The intermediate layer composition (layer II) in specimens with volume ratio of 1.25 and 3 was a single-phase Al₁₂Mg₁₇, while for the case of volume ratio 5.25 this sub-layer consisted of Al₁₂Mg₁₇/(Mg) eutectic dispersed in Al₁₂Mg₁₇ intermetallic. The results of this research showed that in low melt/solid volume ratios, diffusion-reaction was the dominant mechanism for formation of Al-Mg intermetallic. However, when V _m/V _s and the melt/solid insert contact time increased, the dominant mechanism of Al-Mg intermetallics changed to fusion-solidification due to increase in surface melting of the solid insert. Also the results of push-out tests showed that shear strengths of the interface decrease from 27.1 to 15.1 and 8.3 MPa for the Al/Mg couples prepared at 1.25, 3, and 5.25 V _m/V _s respectively.     

Effect of HEA/Al composite interlayer on microstructure and mechanical property of Ti/Mg bimetal composite by solid-liquid compound casting

In this study,HEA/AI composite interlayer was used to fabricate Ti/Mg bimetal composites by solidliquid compound casting process.The Al layer was prepared on the surface of TC4 alloy by hot dipping,and the FeCoNiCr HEA layer was prepared by magnetron sputtering onto the Al layer.The influence of the HEA layer thickness and pouring temperature on interface evolution was investigated based on SEM observation and thermodynamic analysis.Results indicate that the sluggish diffusion effect of HEA can ...     

铝/钛异种金属旁路分流MIG电弧熔钎焊特性

以1 mm厚6061铝合金与TC4钛合金板为试验材料,进行旁路分流MIG电弧熔钎焊工艺试验,得到均匀美观的焊缝成形.分别采用金相显微镜、扫描电镜、万能拉伸试验机进行研究.结果表明,界面层上方金属间化合物以柱状晶形式存在,呈现短而密集的状态.界面层靠近钛侧易形成AlTi,而界面层靠近铝侧易形成Al₃Ti,TiSi₂等金属间化合物,由于焊接过程中熔池内部温度的变化不均,会使界面层中出现Al₁₁Ti₅过渡相.拉伸试验表明,接头最高抗剪强度达182.6 MPa,约为铝母材的97.6%,断裂发生在铝母材热影响区,断口出现一定量的颈缩.