Effects of Mg content on microstructure, mechanical properties and fracture behavior of wrought Al–8Si–(<0.01–1.32)Mg alloy sheets in T6 temper

In this paper, the effects of the Mg content on the microstructure, mechanical properties and fracture behavior of wrought Al–8Si–(<0.01–1.32)Mg (mass fraction, %) alloy sheets in T6 temper were systematically studied by OM, SEM/EDS, EBSD, LSCM, DSC, TEM and tensile tests. The results show that the size of Si particles decreased slightly with the increase of Mg content, and the recrystallized grain size of experimental alloy sheets was refined from about 16 µm to about 11 µm. The size of β" phases did not change obviously, but its volume fraction increased gradually and then became stable. When Mg content was 1.32%, there were many associated aggregation areas of Mg2Si particles and Si particles in alloy sheet. In addition, the strength of experimental alloy sheets showed an initial increase followed by a slight decrease as the Mg content increased, while the elongation gradually decreased. The finite element model accurately predicted the yield strength of Al–8Si–(<0.01–1.32)Mg alloy sheets in T6 temper, and the model was able to quantify the contribution of various strengthening mechanisms to the yield strength of the alloy sheets. The predicted results were in good agreement with the actual measured results. The tensile fracture mode of Al–8Si alloy sheet was ductile fracture. When Mg content was greater than 0.51%, the fracture pattern of the sheets comprised a combination of ductile and brittle fractures. With the increase of Mg content, the number of dimples in experimental alloy sheets increased slightly, the depth gradually became shallow and the size slightly decreased. Meanwhile, most secondary cracks on the surface of the Al–8Si alloy sheets after tensile fracture bypassed the Si particles and a few sheared the Si particles. With the Mg content gradually increasing to 0.78%, the number of Si particles sheared by secondary cracks gradually increased. However, When Mg content was 1.32%, the intergranular fracture phenomenon of Al–8Si–1.32Mg in T6 temper was weakened or even disappeared. There were multiple particles embedded in the same dimples in the tensile fracture. The particles in the associated aggregation areas were more easily broken.