Effect of solution treatment on microstructure and mechanical properties of as-cast Al-12Si-4Cu-2Ni-0.8Mg-0.2Gd alloy

Effect of solution treatment on microstructure and mechanical properties of Al-12Si-4Cu-2Ni-0.8Mg-0.2Gd alloy was investigated. Results show the Si particles become stable and more intermetallic compounds dissolve in the matrix after solution treatment at 500 degrees C for 2 h followed by 540 degrees C for 3 h (T4). The skeleton-like Al3CuNi develops into two parts in the T4 alloy: one is Al3CuNi which has the framework shape; the other is intermetallics including the Al3CuNi (size: 5-10 mu m) and AlSiCuNiGd phases (size: <= 5 mu m) with complex structure. Adding 0.2% Gd can improve the mechanical properties of the alloys after two-step solution treatment (500 degrees C/2 h followed by 540 degrees C/3 h), the hardness of the alloy increases from 130.9 HV to 135.8 HV compared with the alloy with one-step solution treatment (500 degrees C/2 h), the engineering strength increases from 335.45 MPa to 352.03 MPa and the fracture engineering strain increases from 1.44% to 1.67%.