Study on Key Joining Technology and Test Method of Steel/Al Hybrid Structure Body-in-White

Green and low carbon promote the application and development of light-weight materials in body-in-white. Large-scale die-casting Al alloy (DCAA) and high-strength thermo-formed steel sheet (TFSS) have put forward higher requirements for the application of joining technology of high-strength steel/Al dissimilar materials. Taking the new die-casting Al alloy body as an example, this paper systematically studies the progress of the latest joining methods of steel/Al dissimilar material with combination of two-layer plate and three-layer plate. By analyzing the joining technologies such as FSPR, RES, FDS and SPR, the technology and process characteristics of steel/Al dissimilar material joining are studied, and the joining technical feasibility and realization means of different material combination of the body are analyzed. The conditions of material combination, material thickness, material strength, flange height, preformed holes and joint spacing for achieving high-quality joining are given. The FSPR joining technology is developed and tested in order to meet with the joining of parts with DCAA and TFSS, especially for the joining of three-layer plates with them. It finds the method and technical basis for the realization of high quality joining of dissimilar materials, provides the early conditions for the application of large DCAA and TFSS parts in body-in-white, and meets the design requirements of new energy body. .

Corrosion and tribocorrosion behaviors of AISI 316 stainless steel and Ti6Al4V alloys in artificial seawater

The corrosion and tribocorrosion behaviors of AISI 316 stainless steel and Ti6Al4V alloys sliding against Al2O3 in artificial seawater using a pin-on-disk test rig were investigated. And the synergistic effect between corrosion and wear was emphatically evaluated. The results show that the open circuit potentials of both alloys drop down to more negative value due to friction. The corrosion current densities obtained under tribocorrosion condition are much higher than those under corrosion-only condition. Friction obviously accelerates the corrosion of the alloys. The wear loss for both alloys is larger in seawater than that in pure water. Wear loss is obviously accelerated by corrosion. And AISI 316 stainless steel is less resistant to sliding damage than Ti6Al4V alloy. The synergistic effect between wear and corrosion is a significant factor for the materials loss in tribocorrosion. In this surface-on-surface contact geometry friction system, the material loss is large but the ratio of wear-accelerated-corrosion to the total wear loss is very low.

Microstructures and mechanical properties of metal inert-gas arc welded Mg-steel dissimilar joints

The joining of Mg alloy to steel was realized by metal inert-gas arc welding, and the weld thermal cycle characteristics and Mg-steel joints were investigated. The results show that the temperature distribution in the joints is uneven. Mg alloy welds present a fine equiaxed grain structure. There exists a transition layer consisting mainly of AlFe, AlFe3 and Mg（Fe, Al）2O4 phases at Mg/steel interface, and it is the weakest link in Mg？steel joints. The welding heat input and weld Al content have the significant effect on the joint strength. The joint strength increases with increasing the heat input from 1680 J/cm to 2093 J/cm, due to promoting Mg/steel interface reaction. When weld Al content is increased to 6.20%, the joint strength reaches 192 MPa, 80% of Mg alloy base metal strength. It is favorable to select the suitable welding heat input and weld Al content for improving joint strength.

Effect of welding process on the microstructure and properties of dissimilar weld joints between low alloy steel and duplex stainless steel

To obtain high-quality dissimilar weld joints, the processes of metal inert gas （MIG） welding and tungsten inert gas （TIG） welding for duplex stainless steel （DSS） and low alloy steel were compared in this paper. The microstructure and corrosion morphology of dissimilar weld joints were observed by scanning electron microscopy （SEM）; the chemical compositions in different zones were detected by en- ergy-dispersive spectroscopy （EDS）; the mechanical properties were measured by microhardness test, tensile test, and impact test; the corro- sion behavior was evaluated by polarization curves. Obvious concentration gradients of Ni and Cr exist between the fusion boundary and the type II boundary, where the hardness is much higher. The impact toughness of weld metal by MIG welding is higher than that by TIG weld- ing. The corrosion current density of TIG weld metal is higher than that of MIG weld metal in a 3.5wt% NaC1 solution. Galvanic corrosion happens between low alloy steel and weld metal, revealing the weakness of low alloy steel in industrial service. The quality of joints pro- duced by MIG welding is better than that by TIG welding in mechanical performance and corrosion resistance. MIG welding with the filler metal ER2009 is the suitable welding process for dissimilar metals jointing between UNS $31803 duplex stainless steel and low alloy steel in practical application.

SUS441不锈钢/Al金属间化合物微叠层复合板的界面结构与力学性能

采用“表面预处理—交替层叠—热轧复合—热处理”的工艺流程制备了SUS441不锈钢/Al金属间化合物微叠层复合板。利用光学显微镜、X射线衍射仪、扫描电子显微镜等检测与表征方法研究了热处理温度对复合板界面形貌、微观组织、物相组成、维氏硬度、拉伸性能的影响。结果表明:复合板界面结合良好;热处理后,固–液反应界面氧化严重,易导致界面分层而开裂;固–固、固–半固、固–液热处理后,金属间化合物层由均匀层和两相层组成,均匀层的物相组成为Fe_(2)A_(15),两相层的物相组成为Fe_(4)Al_(13)和Al_(13)Cr_(2),且两相层具有韧性特征,固–半固反应所得到的复合板的综合力学性能最佳。

Microstructural characteristics of joint region during diffusion-brazing of magnesium alloy and stainless steel using pure copper interlayer

A novel joining method,double-stage diffusion-brazing of an AZ31 magnesium alloy and a 304L austenitic stainless steel,was carried out using a pure copper interlayer.The solid-state diffusion bonding of 304L to copper was conducted at 850 ℃ for 20 min followed by brazing to AZ31 at 520 ℃ and 495 ℃ for various time.Microstructural characteristics of the diffusion-brazed joints were investigated in detail.A defect free interface of Fe-Cu diffusion area appeared between the Cu alloy and the 304L steel.Cu-Mg reaction products were formed between AZ31 and Cu alloys.A layered structure including AZ31/Cu-Mg compounds/Cu/Fe-Cu diffusion layer/304L was present in the joint.With time prolonging,the reduction in the width of Cu layer was balanced by the increase in the width of Cu-Mg compounds zone.Microhardness peaks in the zone between AZ31 and Cu layer were attributed to the formation of Mg-Cu compounds in this zone.

Microstructure and mechanical properties of friction welds between TiA l alloy and 40Cr steel rods

Direct friction welding of Ti Al alloy to 40 Cr steel rods was conducted, and the microstructure and mechanical properties of the resultant joints in as-welded and post-weld heat treatment（PWHT） states were investigated. The martensitic transformation occurred and brittle Ti C phase formed near the interface due to C agglomeration, which degraded the joint strength and increased the microhardness at the interface in as-welded state. Feathery and Widmanstatten structure generated near the interface on Ti Al alloy side. After PWHT at 580 °C and 630 °C for 2 h, the sorbite formed and C dispersed at the interface, leading to the increase of the joint strength from 86 MPa in as-welded state to 395 MPa and 330 MPa, respectively. The heat-treated specimen fractured with quasi-cleavage features through the zone 1 mm away from the interface on TiA l alloy side, but the as-welded specimen failed through the interface.

Contact reactive brazing of Al alloy/Cu/stainless steel joints and dissolution behaviors of interlayer

Contact reactive brazing of 6063 Al alloy and 1Cr18Ni9Ti stainless steel was researched by using Cu as interlayer. Effect of brazing time on microstructure of the joints, as well as the dissolution behaviors of Cu interlayer was analyzed. The results show that the product of reaction zone near 1Cr18Ni9Ti is composed of Fe2Al5, FeAl3 intermetallic compound （IMC）, and Cu-Al IMC; the near by area is composed of Al-Cu eutectic structure with Al （Cu） solid solution. With increasing the brazing time, the thickness of IMC layer at the interface increases, while the width of Al-Cu eutectic structure with Al（Cu） solution decreases. Calculation shows the dissolution rate of Cu interlayer is very fast. The complete dissolution time is about 0.47 s for Cu interlayer with 10 μm in thickness used in this study.

Electron beam welding of 304 stainless steel to QCr0.8 copper alloy with copper filler wire

Electron beam welding （EBW） of 304 stainless steel to QCr0.8 copper alloy with copper filler wire was carried out. Orthogonal experiment was performed to investigate the effects of process parameters on the tensile strength of the joints, and the process parameters were optimized. The optimum process parameters are as follows：beam current of 30 mA, welding speed of 100 mm/min, wire feed rate of 1 m/min and beam offset of-0.3 mm. The microstructures of the optimum joint were studied. The results indicate that the weld is mainly composed of dendriticαphase with little globularεphase, and copper inhomogeneity only occurs at the top of the fusion zone. In addition, a melted region without mixing exists near the weld junction of copper side. This region with a coarser grain size is the weakest section of the joints. It is found that the microhardness of the weld decreases with the increase of the copper content in solid solution. The highest tensile strength of the joint is 276 MPa.

Welding of shape memory alloy to stainless steel for medical occluder

Dissimilar metal joining between NiTi shape memory alloy（SMA） and stainless steel was conducted.A cluster of NiTi SMA wires were first joined with tungsten inert gas（TIG） welding process,then the NiTi SMA TIG weld was welded to a stainless steel pipe with laser spot welding process.The microstructure of the welds was examined with an optical microscope and the elemental distribution in the welds was measured by electron probe microanalysis（EPMA）.The results show that TiC compounds dispersively distribute in the NiTi SMA TIG weld.However,the amount of TiC compounds greatly decreases around the fusion boundary of the laser spot weld between the NiTi SMA and stainless steel.Mutual diffusion between NiTi shape memory alloy and stainless steel happen within a short distance near the fusion boundary,and intermetallic compounds such as Ni3Ti＋（Fe,Ni）Ti appear around the fusion boundary.

Al-Sn-Si/Al/steel层状复合材料的变形复合行为及机理

通过室温轧制和压缩变形法 ,研究了坯料厚度、变形率、表面状态等工艺因素对Al Sn Si/Al/steel层状复合材料粘结行为的影响 ,提出了变形复合模型。结果表明 :压缩变形法难以复合该层状复合材料 ,而当轧制变形率达到 4 5 %时 ,Al Sn Si/Al/steel就能获得良好的粘结效果 ,随坯料厚度的减小及变形率的增加 ,粘结强度亦增加 ;表面多向抛磨有利于改善粘结状态。粘结界面形貌表明 ,硬质Si粒子明显阻碍表面粘结 ,两接触表面塑性变形和流动是导致粘结的主要机制。

Al/Mg搅拌摩擦点焊–钎焊接头的微观组织与拉伸剪切性能研究

采用搅拌摩擦点焊–钎焊工艺进行2A14铝合金和AZ31镁合金的连接,使用扫描电子显微镜(Scanning electron microscope,SEM)、能量色散谱(Energy dispersive spectroscopy,EDS)和X射线衍射仪(X–ray diffraction,XRD)研究不同参数下接头的微观组织、化学成分及物相组成,采用电子万能试验机对接头进行拉伸剪切性能测试。研究结果表明,搅拌区主要由Al–Mg系金属间化合物和少量MgZn相、MgZn_(2)相组成;热力影响区主要由富Zn固溶体和Mg_(7)Zn_(3)相组成;热影响区靠近铝合金处的锌钎料没有与其他元素发生反应,靠近镁合金处的锌钎料与镁元素发生反应,生成了Mg–Zn系金属间化合物。当轴肩下压量为0.5 mm,搅拌头旋转速度为950 r/min时,接头的拉伸剪切载荷达到最大值7.6 kN。

Microstructural evolution and mechanical properties of friction stir-welded C71000 copper–nickel alloy and 304 austenitic stainless steel

Dissimilar joints comprised of copper–nickel and steel alloys are a challenge for manufacturers in modern industries, as these metals are not thermomechanically or chemically well matched. The present study investigated the effects of tool rotational speed and linear speed on the microstructure and mechanical properties of friction stir-welded C71000 copper–nickel and 340 stainless steel alloys using a tungsten carbide tool with a cylindrical pin. The results indicated that a rotational-to-linear speed ratio of 12.5 r/mm did not cause any macro defects, whereas some tunneling defects and longitudinal cracks were found at other ratios that were lower and higher. Furthermore, chromium carbide was formed on the grain boundaries of the 304 stainless steel near the shoulder zone and inside the joint zone, directing carbon and chromium penetration toward the grain boundaries. Tensile strength and elongation percentages were 84% and 65% of the corresponding values in the copper–nickel base metal, respectively.

Microstructure characteristics and mechanical properties of steel stud to Al alloy by CMT welding-brazing process

Cold metal transfer （CMT） welding of nickel-coated Q235 steel studs with 606l Al alloy was carried out using ER4043 as filler metal. The welding process was stable, and appearance of weld formed well without surface defect under the parameters of welding current 121 A, welding voltage 15.4 V and welding speed 6 r/min. The microstructure of fiUer metal was analyzed by means of scanning electron microscopy. The filler metal and 6061 Al alloy were fused to form fusion welding interface, the fusion zone had a good bonding without any micro defect. The steel stud did not melt and brazing interface was formed between the filler metal and steel stud. Two different reaction layers existed in the brazing interface, the Fe2Al5 layer about 10 -12 p^m formed near the steel stud side, and the other layer was mainly composed of FeAl3. Nickel-rich zone was formed in the root toe area of the fillet weld, which was mainly composed of Al3Ni2. The tensile tests showed that the maximum shearing strength of the joints was 129 MPa. The joint was brittle fractured in the intermetallic compound layer where plenty of FeAl3 were distributed continuously.

Microstructure and mechanical properties of friction stir weld of dissimilar AZ31-O magnesium alloy to 6061-T6 aluminum alloy

Dissimilar friction stir welding between AZ31-O Mg and 6061-T6 Al alloys was investigated. 3 mm thick plates of aluminum and magnesium were used. Friction stir welding operations were performed at different rotation and travel speeds. The rotation speeds varied from 600 to 1400 r/min, and the travel speed varied from 20 to 60 mm/min. Defect-free weld was obtained with a rotation speed of 1000 r/min and travel speed of 40 mm/min. Metallographic studies showed that the grain size in the stir zone is much finer than that in the base metals. Complex flow pattern was formed in the stir zone. Microhardness measurement revealed an uneven distribution in the stir zone. Tensile test results indicated that the tensile strength of the welded specimen is about 76% of AZ31 Mg alloy and 60% of the 6061 Al alloy in tensile strength. SEM fracture surface image of the welded specimen indicated that the welded specimen failed through brittle-mode fracture.

Improving pulsed laser weldability of duplex stainless steel to 5456 aluminum alloy via friction stir process reinforcing of aluminum by BNi-2 brazing alloy

Effects of laser pulse distance and reinforcing of 5456 aluminum alloy were investigated on laser weldability of Al alloy to duplex stainless steel (DSS) plates. The aluminum alloy plate was reinforced by nickel-base BNi-2 brazing powder via friction stir processing. The DSS plates were laser welded to the Al5456/BNi-2 composite and also to the Al5456 alloy plates. The welding zones were studied by scanning electron microscopy, X-ray diffractometry, micro-hardness and shear tests. The weld interface layer became thinner from 23 to 5 μm, as the laser pulse distance was increased from 0.2 to 0.5 mm. Reinforcing of the Al alloy modified the phases at interface layer from Al-Fe intermetallic compounds (IMCs) in the DSS/Al alloy weld, to Al-Ni-Fe IMCs in the DSS/Al composite one, since more nickel was injected in the weld pool by BNi-2 reinforcements. This led to a remarkable reduction in crack tendency of the welds and decreased the hardness of the interface layer from ~950 HV to ~600 HV. Shear strengths of the DSS/Al composite welds were significantly increased by ~150%, from 46 to 114 MPa, in comparison to the DSS/Al alloy ones.

Effects of welding parameters and tool geometry on properties of 3003-H18 aluminum alloy to mild steel friction stir weld

Defect-free butt joints of 3003 Al alloy to mild steel plates with 3 mm thickness were performed using friction stir welding （FSW）. A heat input model reported for similar FSW was simplified and used to investigate the effects of welding speed, rotation speed and tool shoulder diameter on the microstructure and properties of dissimilar welds. The comparison between microstructure, intermetallics and strength of welds shows the good conformity between the results and the calculated heat input factor （HIF） achieved from the model. The joint strength is controlled by Al/Fe interface at HIF of 0.2-0.4, by TMAZ at HIF of 0.4-0.8 and by intermetallics and/or defects at HIF0.8.

Modeling and optimizing of steel and mushy Al-28Pb alloy bonding

The bonding of steel and mushy Al 28Pb alloy was studied. The relationship model about preheat temperature of steel plate, solid fraction of mushy Al 28Pb alloy, rolling speed and interfacial shear strength of the bonding plate was established by artificial neural network perfectly. This model can be optimized by a genetic algorithm, and the optimum bonding parameters for the largest interfacial shear strength are: 546 ℃ for preheat temperature of steel plate, 43.5% for solid fraction of mushy Al 28Pb alloy and 8.6 mm/s for rolling speed, and the corresponding largest interfacial shear strength of bonding plate is 70.3 MPa. [

Nickel-coated Steel Stud to Aluminum Alloy Joints Made by High Frequency Induction Brazing

Nickel-coated 45 steel studs and 6061 aluminum alloy with 4047 A1 alloy foil as filler metal were joined by using high frequency induction brazing. The microstrueture of Fe/A1 brazed joint was studied by means of optical microscopy （OM）, scanning electron microscope （SEM）, energy dispersive X-ray （EDX）, and X-ray diffraction （XRD）. Results showed that 45 steel stud and 6061 aluminum alloy could be successfully joined by high frequency induction brazing with proper processing parameters. The bonding strength of the joint was of the order of 88 MPa. Ni coating on steel stud successfully avoided the generation of Fe-AI intermetallic compound which is brittle by blocking the contact between A1 and Fe. Intermetallic compounds, i e, AI3Ni2, AlmNi0.9 and A10.3Fe3Si0.7 presented in AI side, FeNi and Fe-A1-Ni ternary eutectic structure were formed in Fe side. The micro-hardness in intermetallic compound layer was 313 HV. The joint was brittle fractured in the intermetallic compounds layer of A1 side, where plenty of A13Ni2 intermetallie compounds were distributed continuously.

Microstructure and corrosion resistance of Fe-Al intermetallic coating on 45 steel synthesized by double glow plasma surface alloying technology

A binary Fe-Al alloyed layer was synthesized on 45 steel by means of double glow plasma surface alloying technique. The corrosion-resisting layer prepared is composed of a sedimentary layer and a diffusion layer, with a total thickness of about 180 μm. The aluminum content of the alloyed layer shows gradual change from surface to the inside of substrate. The ideal profile is beneficial to the metallurgical bonding of the surface alloying layer with substrate materials. The microstructure of both layers consists of the Fe-Al intermetallic compound, which is FeAl with B2 structure in the sedimentary layer and Fe3Al with incompletely ordered DO3 structure in the diffusion layer. The protective film exhibits high micro-hardness. In comparison with the substrate of 45 steel, the corrosion resistance of the aluminized sample is much higher in 2.0% Na2S and 0.05 mol/L Na2SO4 + 0.5 mol/L NaCl mixed solutions.