Microstructure And Properties Of The Welding Joint Filled With Er Microalloying Al-Mg Welding Wires

Aluminum alloys,typical structural material,are widely applied in aerospace,marine engineering,and vehicle engineering,due to high specific strength,specific rigidity,good corrosion resistance,and low density.Welding is a fabrication process that joins materials,usually metals,by using high heat to melt the parts together and allowing them to cool,causing fusion.Generally,the welding joints for Aluminum alloys,are prepared by traditionally commercial Al-Mg wires,such as ER5183,ER5356 and ER5556 et al.However,these welding wires are difficult to meet the requirements of high strength and good corrosion resistance.Moreover,in many conditions,post-weld heat treatment cannot be implemented due to the unheatable host material,which sets a higher request to the development of welding wire.The addition of inexpensive rare earth Er in aluminum alloy welding wires can improve the microstructure,mechanical properties and corrosion resistance of welding joints.As a result,microalloying aluminum alloys gradually become research focus.In this work,Al-5.5Mg-1Zn and Al-5Mg-0.8Mn welding wires containing different contents of Er were successfully prepared by casting and multi-rolling process,and the welding wires were applied for tungsten inert gas?TIG?welded 7075-T651 and 5083-H116 aluminum alloys.The mechanical performance testing,corrosion resistance testing,optical microscop?OM?,scanning electron microscopy?SEM?,x-ray diffraction?XRD?,transmission electron microscopy?TEM?and electron backscattering diffraction?EBSD?were employed to investigate the effect of Er on the microstructure,mechanical properties and corrosion resistance of welding joints.This work can provide theoretical and experimental rationale for the Er microalloying Al-Mg welding wires.The main results are as follows:?1?A small amount of Er exists in the form of solid solution in the welding joints.When the Er content in the welding wire up to 0.2wt%,Er aggregates in the solid-liquid interface during solidification after welding,and a primary Al₃Er phase with L1₂ structure forms.This phase can serve as a heterogeneous nucleation to refine the grain size of the welding joints.In the natural aging process,Er dissolved in the matrix prefers to exsolute and induces the formation of nano-Al₃Er precipitated in the welding joints.?2?The primary Al₃Er phase can also refine the dendrites of the welding joints,which shortens the diffusion distance of Mg and Zn atoms in the welding joints,and limits the formation of intermetallic compounds.Therefore,the dispersed distribution of??Mg₅Al₈?phase and T[Mg₃₂?Al,Zn?₄₉]phase along the grain boundaries in welding joints can be refined.The mechanical properties and corrosion resistance of welding joints are significantly improved.?3?A large number of coarse T phases continuously distributed in the welding joints of7075 aluminum alloy welded with Al-5.5Mg-1Zn welding wire,which results in poor mechanical properties and corrosion resistance of the welds.For Al-5.5Mg-1Zn-0.6Er welding wires,the grains of the welding joint are significantly refined,as well as T phases.Therefore,the mechanical properties and corrosion resistance of 7075 welding joints are greatly improved.?4?For the 5183 aluminum alloy welding joints using Al-5Mg-0.8Mn-0.4Er welding wires,the ultimate tensile strength of the welding joints reaches 250MPa,with a welding coefficient of 82.1%.For the 7075 aluminum alloy welding joints using Al-5.5Mg-1Zn-0.6Er welding wires,the ultimate tensile strength of 390MPa can be obtained,which is equivalent to71.5%of the base material.Meanwhile,the slow stress corrosion testing shows that the 7075welding joints has the ultimate tensile strength of 433MPa and undergoes 21.5h before failure in 3.5wt%NaCl solution.For 7xxx aluminum alloy welding,Al-5.5Mg-1Zn-0.6Er should be a potential composition of welding wire,which can achive both of excellent mechanical properties and corrosion resistance.