Metallurgical analysis of laser powder bed-fused Al-Si-Mg alloys: Main causes of premature failure

AlSi7Mg and AlSi10Mg are the most used alloys to manufacture Laser Powder Bed Fusion lightweight components. These products have high specific strengths but a sometimes-limited ductility. Several direct aging and T6 heat treatments were applied to as-built alloys to solve the problem and optimise their tensile properties. Investigations about causes of premature failure in AlSi7Mg and AlSi10Mg tensile samples were performed in the as-built, direct aged (200 & DEG;C x 4h) and T6 (solution heat treatment at 505 & DEG;C x 4h followed by aging at 175 & DEG;C) treated conditions. In as built and direct aged samples, laser scan track boundaries affected the crack propagation and, consequently, the elongation values in each analysed condition. Higher elongation values were obtained when the crack predominantly propagates within the heat affected zones and along the laser scan track boundaries. After T6 treatment, defects and needle-like & delta;-Al5FeSi intermetallic particles are observed contributing to the crack nucleation of samples. The laser scan track boundaries remain after the solution heat treatment and redirect the crack propagation in T6 Al-alloys. The effects of precipitation hardened & alpha;-Al matrix on the fracture mechanisms were also investigated in AlSi7Mg samples.