Build-Height Influence on Electrical Conductivity and Mechanical Properties of LPBF-Manufactured AlSi7Mg Alloy: Role of Networked and Composite-Like Microstructures

This study presents the variations in electrical conductivity in 300 mm-tall AlSi7Mg samples produced by laser powder bed fusion, a height greater than that typically examined in previous studies. Electrical conductivity was correlated with the microstructure and mechanical properties in both as-built and heat-treated specimens. Two-dimensional image analysis confirmed a density of ~ 99 pct in the as-built state with pore diameters ranging from 2 to 15 μm, which shifted slightly after exposure to 505 °C/4 h (resulting in a density of 97.7 pct). The limited porosity exhibited negligible impact on electrical conductivity. In the as-built state, an electrical conductivity gradient was developed along the build height due to the precipitation and sub-grain structures present in the bottom regions, compared to a supersaturated solid solution presents in the top regions. Direct aging at temperatures between 175 and 225 °C enhanced the electrical conductivity by 20 to 35 pct, primarily due to precipitation phenomena and coarsening of the Si-eutectic network (especially at temperatures above 200 °C). Following solution treatment, the Si-decorated α-Al cells transformed into a composite-like structure in which Si particles were embedded in the Al matrix, leading to 27 to 31 pct increase in electrical conductivity and an 8 to 15 pct increase in strength. A proportional relationship between the electrical conductivity-to-yield strength ratio and elongation was also identified, emphasizing the strong dependence between microstructure, electrical conductivity, and mechanical behavior.