Microstructure And Properties Of 6082 Aluminum Alloy Metal Inert-gas Welded Joint

With its high specific strength,good corrosion resistance and processing performance,6082 aluminum alloy has become a structural material that is used more in the transportation field.While achieving lightweight,it also responds to the national call for energy conservation and emission reduction.The manufacture of various 6082 aluminum alloy structural parts,such as automobile wheels,high-speed rail car bodies,etc.,cannot be separated from welding technology.In actual production,MIG welding has become the most important welding method for 6082 aluminum alloy due to its high production efficiency,simple operation and strong applicability.However,the current research on MIG welding of 6082 aluminum alloy,especially the medium and thick aluminum alloy,is mostly still at a relatively simple stage,and there is a lack of further exploration of the joint structure and performance.The purpose of this paper is to solve these problems.In this paper,the butt and cruciform joining of 6082-T651 aluminum alloys was conducted by MIG welding with ER5087 filler wire and the thickness of the plates is 12 mm and 15 mm,respectively.The formation mechanism and microstructure characteristics of the weld seam under the two types of joints,as well as the element distribution in different areas of the joints,are studied.The influences of different welding process parameters on weld formation,joint mechanical properties,corrosion resistance and electrochemical properties are investigated.The research results are as follows:Through the multi-pass welding experiment of 6082-T651 aluminum alloy,it is found that different areas of the joint have different microstructure and texture characteristics.The weld edge is columnar crystal zone,and the weld center is equiaxed dendrite.The microstructure of the base metal(BM)and the heat affected zone(HAZ)is basically the same,and the thick Al-Si-Fe-Mn phase is distributed on the aluminum matrix along the rolling direction.The weld seam has a typical cube texture,and the grain boundary misoriented angle is mainly low-angle grain boundary.The closer to the center of the weld seam,the weaker the texture feature,the higher the proportion of high-angle grain boundaries.The maximum tensile strength of welded joint is 232 MPa and the bending angle of the root bend sample reaches 90 o without cracks.The microhardness of the joint is distributed symmetrically along the weld center,and there are two softening zones: weld zone(WZ)and over-aging zone.Corrosion is mainly local corrosion around the second phase caused by different potential.The order of corrosion resistance of each area is BM>HAZ>WZ.Through the 6082-T651 aluminum alloy cruciform welding experiment by ship welding,it is found that when the welding heat input is low,there are unfused welding defects at the root of the weld,and the weld depth and weld width are small.With the increase of the heat input,the weld crown decreases gradually,and the weld depth and weld width increase.The maximum tensile strength is 239 MPa.The fracture locations are all located in the weld center,starting from the weld root and along the 45 o direction.The fracture shows two fracture modes: ductile fracture and shear fracture.The hardness values of the web and wing plates are symmetrically distributed,and the hardness values of the WZ under different parameters have little difference,ranging from 75 to 81 HV.As the welding heat input increases,the range of the HAZ becomes larger and the hardness value gradually decreases.In the local position of the WZ,there are corrosion cracks with crack-like expansion centered on the void defect and covered with white Al(OH)3 corrosion products.Electrochemical parameters show that the corrosion resistance of each area is the same as that of the butt joint,with the BM being the strongest,followed by the HAZ and the WZ being the worst.