Effect of Mn on microstructures and mechanical properties of Al-Mg-SiCu-Cr-V alloy

In order to improve the performances of the Al-Mg-Si-Cu-Cr-V alloy,various amounts of Mn(0-0.9wt.%) were added.The effect of this Mn on the microstructures and mechanical properties of Al-Mg-Si-Cu-Cr-V alloys in different states,especially after hot extrution and solid solution treatment,was systematically studied using scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),and mechanical tests at room temperature.The results show that 0.2wt.% Mn can both refine the as-cast microstructure of the alloy and strengthen the extrusion+T6 state alloy without damaging the plasticity badly due to the formation of Al 15(FeMn) 3 Si 2 and Al 15 Mn 3 Si 2 dispersoids.Compared with the extrusion+T6 state alloy without Mn addition,the ultimate tensile strength and yield strength of the alloy with 0.2wt.% Mn addition are increased from 416.9 MPa to 431.4 MPa,360.8 MPa to 372 MPa,respectively.The elongation of the extrusion+T6 state alloy does not show obvious change when the Mn addition is less than 0.5wt.%,and for the alloy with 0.2wt.% Mn addition its elongation is still as high as 15.6%.However,when over 0.7wt.% Mn is added to the alloy,some coarse,stable and refractory AlVMn and Al(VMn)Si phases form.These coarse phases can reduce the effect of Mn on the inhibition of re-crystallization;and they retain the angular morphology permanently after the subsequent deformation process and heat treatment.This damages the mechanical properties of the alloy.