Gradient in microstructure and mechanical property of selective laser melted AlSi10Mg

Highlights: • Gradient in microstructure and mechanical property of selective laser melted parts was reported. • The cooling rate of the melt pool was simulated. • The top surface area has a lower degree of crystallinity of Al matrix than that of core area. • Obvious massive sub-boundaries and finer dendrites were found in surface area. • The hardness and wear resistance of the surface is better than the core area. It is known that metal parts can be made stronger, tougher and better wear resistance by introducing gradient microstructure. This work reports the cooling rate of melt pool induced discrepancy in microstructural gradient and element distribution during selective laser melting (SLM), thereby resulting in decrease in microhardness and wear resistance from surface to inside with a range of ∼100 μm of SLM- manufactured AlSi10Mg alloy. The cooling rate in the top surface of melt pool reaches ∼1.44 × 10⁶ K/s, which is much higher than that at the bottom (≤1 × 10³ K/s). Such a difference in cooling rate of melt pool is the main cause for forming gradient microstructure in terms of the distribution of Si particles, dendrite size, sub-grains and sub-boundaries. The variation in microstructure of SLM-produced AlSi10Mg alloy, as a result of gradient cooling rate, has a significant impact on its mechanical properties. Compared with core area, the surface area with a higher cooling rate is composed of finer Si particles, dendritic structure and more sub-boundaries, resulting in higher microhardness and greater wear resistance. The mechanism for formation of gradient microstructure and its influence on the mechanical properties are discussed, which provide new and deep insight into fabricating SLM-produced components with gradient microstructure.