Pulsed laser remelting of A384 aluminum, part I: Measuring homogeneity and wear resistance

The objective of this study is to understand how pulsed laser remelting of aluminum alloy A384 redistributes its surface compositions, and affects its hardness and wear resistance. As a result of each laser pulse, the material experiences rapid heating (melting) and cooling (solidification), which can change the microstructure and degree of chemical homogeneity significantly. These changes in microstructure would manifest themselves as changes in mechanical properties. The proeutectic silicon precipitates found in as-cast A384 melt and disperse into the aluminum matrix during pulsed laser remelting, and do not have sufficient time to grow into large precipitates due to the rapid cooling rate. The result is a more homogeneous surface. The homogeneity is investigated by scanning electron microscope/energy dispersive spectroscopy and two-dimensional power spectral density analysis. Nanoindentation and wear tests at micro- and meso-length scales are applied to identify the effect of element redistribution on hardness and wear resistance. Compared to the base material, the hardness of the pulsed laser remelted surface becomes more uniform, which is an expected consequence of elemental homogenization. The remelted surface exhibits a higher hardness compared with the matrix of the base material, and homogenization is found to improve the wear resistance at both the micro- and meso-length scale.