Effect of isothermal heat treatment on hardness of x7475 alumoinium alloys

Abstract

The heterogeneous nature of microstructure in most as-cast alloys has created the unique properties for an ally before heat treatments. The scanty nature of scholarly articles on the effect of heat treatments on the hardness of new alloys produced from recycled aluminium alloys prompts this investigation. In this work, we upgraded from 3 series to 7 series alloys to form a new material. Previous attempts were also silent on the Alcao Green Letter specifications of the 7 series alloys, hence producing a 7475 alloy that may not be within the Alcao specifications. This paper presents the result of preliminary studies on new experimental X7475 Al-alloy that was produced per Alcoa Green Letter specifications, with variations of Zn (4.0 - 5.0 wt.%), Mg (1.00 - 1.50 wt.%) and Mn (0.025 - 0.075 wt.%), then subjected to microhardness probe under a load of 490.3mN (0.05Hv) and 10sec duration after isothermal and isochronous “O”, T4 and T6 heat treatments. Heating and cooling rates were controlled during heat treatment processes to investigate the effects on the formation of the MgZn2 and other precipitates on the mechanical properties of the alloy. Peak obtainable hardness value of 140.45 Hv and 134.32 Hv are attained within the T6 and T4 conditions in an alloy of 4% and 5% Zn respectively. The increase in wt.% of Zn favours mechanical properties while reverse is the case for Manganese. This result is an indication of the load bearing capacity of our alloy. It has also demonstrated the success in upgrading the 3 series to 7 series alloys from secondary materials. However, the result could be improved on after composition, heat treatments and production route optimization.