Effect of Heat Treatment on the Hardness of Cast EN AC-43000-F (AlSi10Mg) Aluminum Alloy

Abstract

An Heat treatment is an important method for modifying the mechanical properties of heat-treatable cast aluminum alloys. This study experimentally investigates the effects of annealing and T6 heat treatment on the Rockwell hardness of cast EN AC-43000-F (AlSi10Mg) aluminum alloy. The investigated conditions included the as-cast state, annealing at 350 °C for 1.5 h followed by furnace cooling, solution treatment at 540 °C for 2 h followed by water quenching, and artificial aging at 170 °C for 4, 8, and 12 h. The specimens measured 50 × 40 × 10 mm. Hardness was measured using the Rockwell HRF scale in accordance with ASTM E18. For each heat-treatment condition, three independent specimens were evaluated, and the reported hardness values represent their average. The mean hardness of the as-cast alloy was 64.9 HRF. Annealing reduced the hardness to 52.9 HRF, corresponding to an approximately 18.5% decrease relative to the as-cast condition. Following solution treatment and water quenching, the mean hardness increased to 74.4 HRF. Subsequent artificial aging increased the mean hardness to 91.5, 110.4, and 102.5 HRF after 4, 8, and 12 h, respectively. The highest mean hardness was therefore obtained after 8 h at 170 °C. The subsequent decrease after 12 h is consistent with a transition beyond the maximum age-hardening condition; however, without direct microstructural characterization, it cannot be considered conclusive evidence of over-aging. Overall, the results demonstrate that hardness is strongly dependent on thermal history, with T6 treatment producing a substantial increase compared with the as-cast and annealed states.