Effects of heat treatment on non-dendritic grains microstructure and mechanical properties of A356 alloy

W Ishak, Wan Muhammad Sulaimi (2023) Effects of heat treatment on non-dendritic grains microstructure and mechanical properties of A356 alloy. Project Report. Universiti Teknikal Malaysia Melaka, Melaka, Malaysia. (Submitted)

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Abstract

A post-casting thermal treatment such as T6 temper is a normal process in the aluminium alloys foundry for car parts production industry. T6 has three step thermal treatments, solution treatment, quenching and artificial ageing. In addition, a semi-solid processing method will help to increase further the robustness of the alloys. In semi solid processing, the alloy must posseses a thixotropic behaviour of non-dendritic microstructures. Currently, the effects of both processes, T6 heat treatment and semi-solid, on A356 aluminum alloy reported were still lacking. Therefore, objectives of the study are to determine the macro hardness of non-denrtitic grains microstructure A356 alloy and its evolution at each stage of the T6. The non-dendritic microstructure of the A356 feedstock has been prepared via a spiral channel casting. The T6 thermal cycle includes solution treatment at 540℃ for 6 hours, water quenching, and artifical ageing for 6 hours at 180℃. Methods used to perform an inspection of grain microstructure by using microscope ZEISS AX10 and Mitutoyo Rockwell will be used for the hardness test. As results, the macro hardness increased by 42.67 %, from 7.25 RHB to 18.04 RHB and grain size mean areas increased by 5.3 %, that is from 9 μm to 1.4 μm. These values obtained by different tests are significant based on the P-values of T-Test. Furthermore, a direct comparison between the dendritic A356 using direct casting method was also reported. The improvement in strength of alloy after T6 heat treatment is due to elimination of microporosities and rearragement of the allo microstructure.

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