Experimental investigation on tensile properties and yield strength modeling of t5 heat-treated counter pressure cast a356 aluminum alloys

In the present study, experimental investigations on microstructures and tensile properties of an counter-pressure cast (CPC) A356 aluminum alloy under different T5 heat treatment conditions were conducted in the temperature range of 160–200^◦C for 1–48 h. As the T5 heat treatment time increased, both tensile and yield strength of the CPC A356 alloy either continuously increased at 160^◦C until 48 h of heat treatment time or increased until the maximum strength values were achieved and then decreased, showing peak aging behavior at 180 and 200^◦C. Changes in microstructural aspects, such as size and aspect ratio, of the eutectic Si, Mg and Si distribution in the α-Al grain and the stability of intermetallic compounds were found to be negligible during the T5 heat treatments employed in the present study. From high resolution-transmission electron microscope (HR-TEM) analysis, nanosized needle-like β^′′ precipitates were identified in the specimens, showing a significant increase in strength after the T5 heat treatment. Based on the measured tensile properties and observed microstructure changes, a yield strength model was proposed to predict yield strengths of CPC A356 alloys at arbitrary T5 heat treatment conditions. The calculation results of the model showed good agreement with the experimental data obtained in the present study. From the model calculations, the optimal T5 heat treatment time or temperature conditions were suggested.