Effect Of Microalloying Al-5Mg-1Zn Wire On Microstructure And Properties Of Aluminum Alloy Weld

It is well known that aluminum alloy has become one of the indispensable materials in the field of vehicle engineering,marine engineering,aerospace,and other fields,because of its light-weight,high specific strength,and good corrosion resistance.The aluminum alloy joint welded by traditional commercial welding wire is difficult to meet the high strength and high corrosion resistance simultaneously.Therefore,the investigation of microalloyed aluminum alloy welding wire is of great significance.In this dissertation,Al-5Mg-1Zn and Al-5Mg-1Zn-0.3Sc-0.15Zr welding wires with different contents of Mn were prepared by casting and multi-rolling processing.The base metal,such as 7075-T651 and 5083-H116aluminum alloys,was successfully welded by tungsten inert gas welding.The microstructure,corresponding mechanical properties,and the corrosion behavior of welded joints using microalloyed welding wires were investigated by microscopy methods,tensile tests,and corrosion tests.The main results are as following:(1)For the welding joints of 7075 aluminum alloys welded by Al-5Mg-1Zn wires,grains are coarse,and a large number of T phases[Al₃₂(Mg,Zn)₄₉]are continuously distributed in the grain boundary,which results in poor mechanical properties and corrosion resistance.When Mn is introduced into the welding wires,it can be found that the grains of welding joints are refined,as well as the T phase,which improves the mechanical properties and corrosion resistance of 7075 aluminum alloy welding joints.The ultimate tensile strength of joints welded by Al-5Mg-1Zn-0.2Mn wires,raised to 334 MPa and 305 MPa,for normal tensile testing and slow stress corrosion tensile testing,respectively.In addition,there is a threshold for the content of Mn.Under the threshold,increasing Mn element in the welding wire can favor the improvement of the corrosion resistance in welding joints.(2)The joints welded by Sc,Zr,and Mn microalloyed wire and commercial ER5183wires were compared.Microalloyed wires can result in superior mechanical properties and corrosion resistance of the joints.Nanoscale Al₃(Sc,Zr)particles caused by the introduction of0.3_wt%Sc+0.15_wt%Zr,can refine the?-Al grains and have a strong pinning effect on dislocations and sub-grain boundaries.With another addition of 0.4_wt%Mn in welding wires,the 7075 joints can possess the best comprehensive properties.Room temperature and corrosion condition tensile strength of the joints welded by the microalloyed wires are 10.4%and 28.4%higher than those of commercial wire,respectively.The maximum depth of intergranular corrosion is reduced by 67.0%,due to the microalloyed wires.However,higher Mn concentration in welding wires,such as 0.6_wt%Mn,could induce the formation of the Al₆(Mn,Fe)phase,which greatly decreases the corrosion resistance of joints.(3)5083 aluminum alloys were welded by Al-5Mg-1Zn-x Mn(x=0.0,0.2,0.4,and 0.6)wires.Compared with Al-5Mg-1Zn welding wire,the Mn addition in welding wires can effectively refine both the grain and the precipitated phase,which improves the mechanical properties and corrosion resistance of 5083 welded joints.Mn can accelerate the diffusion of Mg and Zn in Al matrix,and reduce the precipitated phase,such as eutectic the?phase.For Al-5Mg-1Zn-0.4Mn welding wires,the slow stress corrosion tensile strength and corrosion failure time of welding joints were increased by 24.6%and 57%,respectively.In addition,excess Mn also has an opposite effect,and x=0.4 is the best concentration of Mn in Al-5Mg-1Zn welding wire for the 5083 aluminum alloy.