Correlating the microstructure and hardness of AlSi10Mg powder with additively-manufactured parts upon in-situ heat-treatments in laser beam powder bed fusion

Abstract

Laser beam powder bed fusion (PBF-LB) of AlSi10Mg has attained technology maturity in various industries. Nevertheless, the manufactured components often require thermal treatments to tailor their microstructures and mechanical properties. Experimental development of suitable thermal cycles for the printed parts is time and energy intensive. However, the characteristic microstructure of parts produced by PBF-LB resembles that of gas-atomised powder. Therefore, this study presents an in-depth investigation on the correlation between the properties of the powder and PBF-LB samples. In-situ heat treatment methodology was deployed to consistently heat-treat the powder and PBF-LB samples using elevated build-plate temperatures (220 - 500 ºC). Scanning electron microscopy revealed Si atoms’ diffusion, followed by eutectic network's disruption and Si particles’ coarsening, with increased build plate temperatures, in both parts and powder. X-ray diffraction and differential scanning calorimetry showed a strong correlation between the powder and parts treated at the same build-plate temperatures. A 500 ºC in-situ heat-treatment temperature reduced the hardness by ∼43% (powder) and ∼52% (printed samples). Nano- and micro-hardness values on the powder and printed samples also exhibited high correlation. Similarities between the powder and part's microstructural changes with temperature were attributed to the similar scale of cooling rates in gas-atomisation and PBF-LB, respectively. The findings in this study pave a clear pathway that experimentation on small batches of powder via ex-situ heat treatments could be efficiently used as a high-throughput method to predict the effect of thermal treatments on printed parts and to design new heat treatment protocols, specifically for PBF-LB materials.