Creep properties and microstructure evolution at 260-300 °C of AlSi10Mg manufactured via laser powder-bed fusion

The aging behavior and creep resistance of eutectic AlSi10Mg (Al-10Si-0.6Mg, wt.%) manufactured by laser powder bed fusion (L-PBF) are studied at 260 and 300 degrees C. The Si phase, which forms a fine interconnected network of 100-200 nm filaments in the as-printed alloy, coarsens into blocky, 2-3 mu m particles after 1 month exposure at 260 and 300 degrees C, with hardness decreasing following a power-law with exponent n = 0.06-0.08. AlSi10Mg with similar to 1 mu m Si particles (achieved by aging at 300 degrees C for 96 h) exhibits creep resistance at 260 and 300 degrees C, for test durations of a few days, comparable to those of (i) cast alloys: hypereutectic Al-Si alloys with coarse Si particles and eutectic Al-Ce, Al-Ce-Ni with much finer, and more coarsening-resistant eutectics phases (e.g., Al11Ce3, Al3Ni); and (ii) L-PBF Al-Mg-Zr alloys. At 260 and 300 degrees C, our L-PBF AlSi10Mg shows a power-law creep behavior with high apparent stress exponents (n(a) = 10-13, higher than n = 4.0 for Al-Mg) for strain rates between similar to 10(-8) and similar to 10(-4) s(-1). Also, a high apparent creep activation energy Q(a) = 256 kJ/mol is measured between 200 and 320 degrees C at 45 MPa, compared to Q = 142 kJ/mol for Al. These high apparent stress exponent and activation energy are consistent with power-law dislocation creep with a threshold stress, originating from load-transfer from the creeping Al(Mg) matrix to non-creeping Si particles.