Effects of minor Ti and Zr addition on the microstructure and mechanical properties of Al-Mg based alloy

Abstract

The main purposes of this study were to prepare alloys in 4 designed compositions (Al-5%Mg, Al-5%Mg-0.2%Zr, Al-5%Mg-0.2%Ti and Al-5%Mg-0.2%Zr-0.2%Ti) by cast process and to investigate the effect of ternary addition of Zr and Ti as well as their combination. Alloys were heat treated at 4 different temperatures: 2500C, 3000C, 4000C and 4500C for 1 hour in an electric furnace. The evolution of microstructure and mechanical properties was investigated for both as cast and heat treatedalloys. Change in dendritic structure due to ternary addition was measured by dendritic arm spacing (DAS)during optical microscopic analysis. Mechanical study includes tensile and hardness property analysis. During as cast analysis, Ti addition shows comparatively more grain refinement (reduces DAS from 25.87 µm to 14.11 µm) than Zr (reduces DAS from 25.87 µm to 18.47 µm). Combination of Ti and Zr shows combined effect in microstructure. On the other hand, Zr increases Tensile strength significantly whereas Ti shows no effect on tensile strength. Alloy containing combination of Zr and Ti gives tensile strength only for Zraddition.But change in hardness value due to ternary addition is very negligible. After heat treated analysis,alloy with combined addition of Zr and Ti shows same as without any addition i.e. dendritic arm spacingdecreases with increasing temperature. Zr retards change in dendritic structure during heating whereas Ti addition results continuous increase in dendritic arm spacing upto 4000C but at 4500C it decreases.Effect of heating on the mechanical properties (tensile and hardness) cannot be identified.