Effect of Substrate Preheating Temperature on Microstructure and Mechanical Properties of AlSi9Mg1ScZr Alloy Prepared by Selective Laser Melting
The effects of substrate preheating temperature on the microstructure and mechanical properties of AlSi9MglScZr alloy samples prepared by selective laser melting(SLM)were investigated.SLM samples were prepared at three different substrate preheating temperatures of 35,85,and 135 ℃,and subjected to microstructure observation and property testing.The results show that the substrate preheating temperature set to 135 ℃ causes the in-situ aging effect of the alloy during the printing process due to the combined effect of the substrate preheating temperature and laser scanning heat input,which promotes the precipitation of elements from the supersaturated solid solution while retaining fine dendrites and Si lattices.Compared with the sample with the substrate preheated at 35 ℃,the nanoscale Mg2Si and Si phases are precipitated significantly more in the α-Al matrix and dendrite boundaries,which improves the strength;however,the precipitation of the micron-scale Fe-rich phase has a negative effect on plasticity.At a substrate preheating temperature setting of 135 ℃,the prepared AlSi9Mg1ScZr alloy exhibits a yield strength of 360 MPa,a tensile strength of 502 MPa,and an elongation of 7%in the 0° direction,and a yield strength of 331 MPa,a tensile strength of 511 MPa,and an elongation of 5.4%in the 90° direction.The microstructure of AlSi9MglScZr alloy prepared by SLM is improved by increasing the substrate preheating temperature and in-situ aging of the SLM samples is achieved during SLM,by which the residual stress is significantly reduced and ultra-high strength AlSi9Mg1ScZr alloy samples can be obtained without subsequent heat treatment.