Study on the fatigue behaviour of selective laser melted AlSi10Mg alloy

Abstract

Selective laser melted (SLM) AlSi10Mg alloy was subjected to high cycle fatigue test to elucidate the effect of microstructural characteristics and sub-microscopic defects in its dynamic behaviour. The microstructure of the processed materials revealed scan tracks on the scanning surface and solidified melt pool/melt pool tracks on the surface in the build direction. The processed material exhibits equi-axed morphology with 〈100〉 fibre texture on the scanned surface and elongated grains preferably 〈100〉 orientation in the build direction. The pore size and distribution in the selective laser melted materials were measured using computed micro-tomography method μ-(CT). The cellular structures constituting 500 nm sized grains were observed. The boundary of the cell was a eutectic mixture of Al and Si while the matrix comprised of primary α-Al as observed from TEM results. The influence of grain morphology, microtexture, pores, and cellular structure on the deformation behaviour of processed materials under cyclic loading were investigated. Load controlled axial fatigue test was conducted at a stress ratio of 0.1 and 25 Hz frequency. Fractographs revealed crack initiation occurred, typically, due to the pores and the Si particles in surface or sub-surfaces. The cellular structures in the microstructure played a significant role in influencing the fatigue crack path, depends on its location in the microstructure. Dislocations in the cellular matrix and dislocation fringes in the cellular boundaries observed through transmission electron microscopy affirms this influence. Anisotropy and shielding gases observed to exhibit no significant influences on the fatigue life of the processed material. The crack initiation and propagation are heavily influenced by surface/subsurface pores and cellular structure as evident from the detailed microscopic investigation made in the present work.