A new SLM-manufactured Al-Si alloy with excellent room and elevated-temperature mechanical properties

The synergistic strengthening of multiple phases has long been an effective method of enhancing conventional metallic structural materials. However, the assembly of solute atoms with high solubility and low diffusion rate into highly stable and high-volume fraction nano-precipitates using the selective laser melting (SLM) technique is challenging. In this study, a new Al-9.0Si-2.8Fe-2.1Mn-1.1Ni (in wt%) alloy was fabricated using the SLM. The melt pool structure of the alloy exhibits equiaxed grain characteristics under optimum parameters, with large volume fractions of in-situ precipitated IMC-Al-15(Fe,Mn,Ni)(3)Si-2 and Si phases within the grains. The alloy demonstrates commendable tensile properties at room temperature (YS 373 +/- 8 MPa, UTS 602 +/- 12 MPa, El 4.2 +/- 0.5 %) and retains excellent strength and ductility as well as creep resistance at elevated temperatures of 400 degrees C (YS 92 +/- 3 MPa, UTS 100 +/- 5 MPa, El 24 +/- 0.7 %, steady-state creep rate similar to 10(-5) s(-1) under 60 MPa). Lamellar nano-Si phases can induce strain delocalization effects and grain boundary relaxation through partial dislocation twinning behavior, thereby coordinating high-temperature deformation. Under large deformations and prolonged creep processes, the transmission of external loads and the evolution of defects (The edge dislocation at interfaces, the stacking faults and deformation twins within the Si phase) effectively transfer stress to low-load-bearing regions, promoting the delocalization of deformation. The abundant second phases within the alloy (IMC and Si phases) hinder dislocation movement and promote dislocation multiplication, maintaining ultra-high deformation resistance and low steady-state creep rate. Due to the absence of heat treatment and the addition of expensive elements, the alloy has wide industrial application potential.