On the heterogeneous cooling rates in laser-clad Al-50Si alloy

Abstract

Abstract The local microstructural heterogeneities in a single layer of laser clad hypereutectic Al-50Si alloy over Al7075 substrate has been studied over different applied laser powers. The general microstructure of the laser clad layer, irrespective of the applied laser power, could be described by three distinctive regions from the deposited bead/substrate interface to the top – i) columnar primary Al-dendritic region, ii) Al-Si near-eutectic region, and iii) non-equilibrium three phase region composed of Si primary particles, fine Al-rich dendrites and interdendritic Al-Si eutectic. A spatial heterogeneity in the cooling rates is inferred within the single clad layer based on the microstructural length scales – the bulk Al-Si shows two orders of magnitude higher cooling rate than interface. A distinct difference in the orientation of the clad microstructure near the bead/substrate interface and size and distribution of Si particles in the deposited layer is seen with different applied laser power. Such microstructural differences have been explained on the basis of the melt pool solidification conditions of the hypereutectic alloy under different laser power.