Study On Microstructure And Mechanical Properties Of Al-Mg-Si Alloy Based On Friction Stir Processing

Friction stir processing（FSP）is a material modification technique that can be used to refine the grain of a material.In this paper,6063 aluminium alloy extruded sheet was used as raw material,and the effects of friction stir processing on the structure and properties of 6063 aluminium alloy were studied under the conditions of specific stirring head rotating speed 1200 r/min,feed speed 90 mm/min and without inclination angle.Different deformation processes and different additive materials were used for friction stir processing experiments.The effects of different stirring heads,multi-pass friction stir processing and addition of SiC composites,fine-grained materials on the macromorphology,microstructures,microhardness and tensile strength of 6063aluminum alloy were investigated.Firstly,the effect of FSP on the microstructure and mechanical properties of 6063aluminum alloy was studied.The grain size of 6063 aluminium alloy is significantly refined and elongation is increased 120%after friction stir processing.The rod-like particles in the base metal isα-Al Fe Mn Si phase.Most of these impurities phaseα-Al Fe Mn Si disappeared after friction stir processing,and the phase in the stirring zone was granular Mg₂Si which was crushed.In order to obtain better properties,the processed materials were heat treated.The optimum aging process was obtained as follows:temperature 180℃,peak aging time 8 h,when the peak hardness of stirring zone was higher than that of base metal.Secondly,the effects of different stirring heads and processing passes on friction stir processing of 6063 aluminum alloy were studied.It was found that the mechanical properties of the material obtained by FSP with 5mm stirring head had the best tensile strength of 277.12MPa and the elongation of 28%,while the tensile strength of the base material was only 210.26MPa and the elongation was 12.5%.With the number of processing passes increases,the hole-like defects in the stirring zone were reduced,the grain size was also smaller,and the grain structure was more and more uniform.Among them,the five-pass FSP had the best effect.The softening zone formed by thermo-mechanically affected zone（TMAZ）and heat-affected zone（HAZ）becomes wider as the number of processing passes,After peak aging,the hardness of stirring zone was recovered even higher than that of matrix,and the hardness of softening zone increased slightly.Finally,the effects of adding SiC and fine-grained materials on the FSP of 6063aluminum alloy were studied.The results show that the lamellar-like structure is formed in the SZ after FSP,and the lamellar-like structure with SiC_p is more obvious than that with fine-grained materials,and the evolution of the lamellar-like structure changes regularly with the increase of passes.The addition of SiC had a great influence on the hardness of stirring zone.After heat treatment,the stirring zone hardness fluctuated obviously in one pass and three passes.The stirring zone hardness of adding fine-grained materials was more uniform than that of SiC materials,and the effect of five passes is the best.The cross-section tensile tests showed that the tensile strength of the specimens of different materials is between 120 MPa and 150 MPa.Only the one-pass tensile test with the addition of SiC fractured at the SiC agglomeration in the stiring zone,and other tensile specimens were fractured in the soft zone consisting of HAZ and TMAZ,which is a plastic fracture breaking from coarsening impurities.