A study of the mechanical properties of an Al-Si-Cu alloy (ADC12) produced by various casting processes

The mechanical properties of an Al-Si-Cu alloy (ADC12), produced using various casting technologies, have been examined experimentally. Four different casting processes were employed, including gravity casting (GC), cold-chamber die-casting (CD), twin rolled continuous casting (TRC) and the Ohno continuous casting process (OCC). Although these produced the same Al-Si-Cu aluminum alloy, different mechanical properties were obtained, in particular microstructural characteristics and dislocation density. The microstructure of GC and CD samples was formed mainly with coarse α-Al phase and needle-shaped Si and Fe based eutectic structures. In contrast, a fine round α-Al phase and tiny eutectic structures were observed for the TRC and OCC samples. Such a change of microstructure was caused by the different casting process parameters, namely injection speed, casting pressure and cooling rate. High internal stress as well as high dislocation density was detected for GC and TRC, caused by the high shrinkage force and high applied rolling force, respectively. Because of the different material properties, the tensile and fatigue strength were altered. A clear Hall-Petch relation with σ _0.2=k _yd ^-0.5+B was obtained, and the fatigue properties were evaluated with the power law dependence σ _a=σ _fN _f ^-b. The mechanical properties obtained were also analyzed in relation to the crystal orientation and lattice mis-orientation angle.