Study On Weldability Of Al-Mg₂Si-Si Alloy

Al-Mg₂Si-Si alloy have exhibited wide application prospects in the fields of automotive and aerospace,due to its light weight,excellent mechanical properties,low thermal expansion,good physical properties,and simple prepare technology.However,as a structural material,the study of weldability has not been reported.In the present thesis,the weldability of Al-Mg₂Si-Si alloy was studied by friction stir welding,tungsten argon arc welding and resistance spot welding.The welding process parameters was optimized through microstructure characterization and mechanical properties test,discussing the mechanism during the welding process.The major research efforts of the present study are as follows:The Al-Mg₂Si-Si alloy present material consists of?-Al phase,Mg₂Si phase and eutectic Si phase.After welding,the phase of the weld nugget region does not change;the change of the alloy composition during the welding process leads to a change in peak value.Under different welding methods,the welded joints on Al-Mg₂Si-Si alloy are consists of the base material zone,the transition zone and the weld nugget zone.After welding,the Mg₂Si particles in the FSW weld nugget area are remarkably refined,and the Thermo-mechanically affected zone has directionality;The nugget region of the RSW welded joint forms equiaxed crystals accompanied by the phenomenon of Mg₂Si segregation,and the nugget region is composed of internal equiaxed crystals and external columnar crystals after the solder is added.After FSW and TIG welding,the texture of the alloy have changed,the texture in the FSW welded joint was enhanced,while the texture in the TIG welded joint was weakenss;the ratio of the low-angle grain boundaries in the present metal region was 57.7%,and the weld nugget area of the FSW and TIG welded joints the low-angle grain boundaries are 83.6%and 34.0%,respectively;the present material contains a large number of needle-shaped?’’precipitates.After welding,the needle-shaped precipitates decrease,forming dislocations and dislocation pile-ups of different densities in the weld nugget.The tensile strength and elongation of the Al-Mg₂Si-Si alloy present material were 122.6MPa and 1.13%,respectively.During the FSW welding process,the tensile strength and elongation of the FSW welded joint were 170MPa and 1.50%,respectively,when the rotation speed was 900rpm,after T6 heat treatment,the tensile strength and elongation increased to245MPa and 1.63%respectively.when the welding current was 135A,the tensile strength and elongation of TIG welded joint were 117.2MPa and 1.21%,respectively.The maximum shear resistance is lower than that of the present metal.After the brazing filler metal is added,the welded joint with superior performance can be obtained at the low current.By comparing the microstructure and mechanical properties of FSW,TIG and RSW welded joints,it can be seen that friction stir welding can obtain welded joints with better performance,which have instructingsignificacefor promoting the engineering and practical application of Al-Mg₂Si-Si alloy.