Mechanisms affecting hardness and electrical conductivity in artificially-aged B319 aluminum alloy

Abstract

Artificial aging is an essential process in the production of Al-Si-Cu-Mg alloys for high-performance applications. The complex phase transformations promoted during this heat treatment tends to influence hardness and electrical conductivity contrarily, prompting significant compromise in the alloy design. Nonetheless, understanding the considerable contrast between electron and dislocation motion enables the informed manipulation of heat treatment parameters for the enhancement of both material properties. Accordingly, this study aimed to investigate the effects of artificial aging on the microstructure, hardness and electrical conductivity of B319 Al alloy, as a function of solidification rate and strontium content. After solution heat treatment, samples were aged at 150, 200 or 250 °C for durations up to 24 h, followed by Rockwell hardness and eddy-current electrical conductivity measurements. In conjunction with qualitative electron microscopy and quantitative transformation curves generated with in-situ x-ray diffraction, the time-dependent property curves were found to correlate with progressive precipitation processes within the Al matrix. Furthermore, the direct juxtaposition of the hardness and conductivity behaviors was used to elucidate the mechanisms affecting either property during artificial aging. Individually, substantial improvements of either +47 HRB or +8% IACS were possible for hardness or conductivity, respectively, within the investigated heat treatments. Yet, the critical analysis in this study supports the strategic design of casting and heat treatment parameters, to produce a suitable combination of both hardness and conductivity in advanced industrial Al alloys.