Influence of the solidification rate on the microstructure and mechanical properties of rapidly solidified Al-Mg-Si alloy

Al-Mg-Si aluminum alloys have excellent strength, toughness and corrosion resistance properties and are widely used in automobile, aerospace and various fields. In this work, the influence of the solidification cooling rate on the microstructure, second phase precipitation, microscopic segregation and mechanical properties of an Al-0.8Mg-0.7Si aluminum alloy was studied in detail. With increasing cooling rate, the secondary dendrite arm spacing gradually decreased from 38.9 μm (105 °C/s) to 9.3 μm (1516 °C/s), and interdendrite segregation gradually weakened. A higher cooling rate refines the α-Al matrix and increases the solid solubility. The hardness of the aluminum alloy increases with increasing cooling rate through solution strengthening and grain refinement strengthening. After deformation heat treatment, the aluminum alloy underwent complete recrystallization, forming uniform equiaxed grains. With increasing cooling rate, the average grain size decreased from 18.6 μm (105 °C/s) to 8.6 μm (1516 °C/s). However, the solution strengthening effect of samples with higher cooling rates decreased significantly because of more pronounced exsolution. With increasing cooling rate, the mechanical properties of the heat-treated aluminum alloy first tended to increase but then decreased, and the samples cooled at 489 °C/s achieved the best strength-ductility match (tensile strength of 230.3 MPa and elongation of 32.7 %) among all the heat-treated samples.