DEFORMATION BEHAVIOR OF A535 ALUMINUM ALLOY UNDER DIFFERENT STRAIN RATE AND TEMPERATURE CONDITIONS

Abstract

Aluminum alloys are a suitable substitution for heavy ferrous alloys in automobile structures. The purpose of this study was to investigate the flow stress behavior of as-cast and homogenized A535 aluminum alloy under various deformation conditions. A hot compression test of A535 alloy was performed in the temperature range of 473-673 K (200-400˚C) and strain rate range of 0.005-5 s-1 using a GleebleTM machine. Experimental data were fitted to Arrhenius-type constitutive equations to find material constants such as n, nʹ, β, A and activation energy (Q). Flow stress curves for as-cast and homogenized A535 alloy were predicted using an extended form of the Arrhenius constitutive equations. The dynamic shock load response of the alloy was studied using a split Hopkinson pressure bar (SHPB) test apparatus. The strain rate used ranged from 1400 s-1 to 2400 s-1 for as-cast and homogenized A535 alloy. The microstructures of the deformed specimens under different deformation conditions were analyzed using optical microscopy (OM) and scanning electron microscopy (SEM).

Obtained true stress-true strain curves at elevated temperatures showed that the flow stress of the alloy increased by increasing the strain rate and decreasing the temperature for both as-cast and homogenized specimens. The homogenization heat treatment showed no effect on the mechanical behavior of the A535 alloy under hot deformation conditions. Hot deformation activation energy for both as-cast and homogenized A535 alloy was calculated to be 193 kJ/mol, which is higher than that for self-diffusion of pure aluminum (142 kJ/mol). The calculated stress values were compared with the measured ones and they showed good agreement by the correlation coefficient (R) of 0.997 and the average absolute relative error (AARE) of 6.5 %. The peak stress and the critical strain at the onset of thermal softening increased with strain rate for both the as-cast and homogenized A535 alloy. Homogenization heat treatment affected the high strain-rate deformation of the alloy, by increasing the peak stress and the thermal softening onset strain compared to those obtained for as-cast specimens. Deformed shear bands (DSBs) were formed in both the as-cast and homogenized A535 alloy in the strain rate range of 2000-2400 s-1.