Correlating Conductivity with Hardness and Density in X7475 Alloys for Development of Linear Hardness Model

Abstract

Hardness (H) may not be sufficed as a property the same way density (ρ) felt short as a measure of physical property, hence there is the need to correlate H with other property (ies). The porous nature of the material, dislocations and addition of constituents to the aluminium matrix affect the conductivity (Ծ) of alloys among other defects. In this article, attempt to fill the gap in recycling beverage can (RBC) for bumper beam applications was made by producing a 7xxx alloy from 3xxx alloy. About 80 % of the raw materials used in this alloy were sourced from secondary means. Stir casting route was adapted. Aluminium (Al) chips, 70 % Cu- 30 % Al, Manganese (Mn) and Magnesium (Mg) were charged in that order. The relationship between Ծ, H and ρ of the new alloy was established in the As-Cast (AC), annealed (O), natural aged (T4) and artificial aged (T6) conditions. In AC, an alloy of Al- 4.0 Zn-1.5Mg-0.35Cu-Mn recorded the peak obtainable Ծ and H of 3.7x107 m/S and 113.06 Hv with a ρ of 2.7464 g/ cm-3. The same alloy recorded peak Ծ and H in the O condition of 3.7x107 m/S and 102.6 Hv, whereas the ρ was 2.752 g/ cm-3. The T4 heat treatment (HT) deviated when the peak Ծ was 3.7x107 m/S, H and ρ were 58.94 Hv and 2.7551 g/ cm-3 respectively. T6 conditioned alloys delivered peak Ծ of 3.7x107 m/S in an alloy of Al- 4.0 Zn-1.5Mg-0.35Cu-Mn with a ρ of 2.7853 g/cm-3 and 60.26 Hv. HT and formation of precipitates were detrimental to Ծ and beneficial to H. Curve fittings were obtained and used in developing linear models for the relationship between H and Ծ within respective conditions unique to the experimental alloys.