Modification mechanism and tensile property of Al-9Si-0.4Mg-0.1Cu alloy

Effect of Heat Treatment on the Microstructure and Mechanical Properties of Al–9Si–0.4Mg–0.1Cu Alloy

“…[ 23 ] In addition, Sr atoms are also enriched at solid–liquid interfaces which inhibit the growth of Si and induces high‐density twinning, leading to eutectic Si growing in different directions and changes from columnar to fibrous. [ 36 ] However, when the content of Al–6Sr–7La increases to a certain extent, a certain volume fraction of Al–Si–Sr–La will formed, which will consume effective Sr and La atoms, resulting in a decrease in the modification effect of eutectic Si, and columnar eutectic Si appears. [ 23,25 ] Meanwhile, it should not be ignored that segregation of eutectic Si is still serious, which will cause uneven stress concentration during the deformation process.…”

“…It should be noted that many nanoprecipitates (Figure 8e) appeared on the eutectic Si, which have been proved to be Sr‐rich phases. [ 36,37 ] During the refinement and modification process, Sr atoms gather in twin‐plane re‐entrant edges to prevent the growth of eutectic Si, leading to the change of the growth direction of eutectic Si. [ 26 ] La can be used as surfactants to facilitate the diffusion of Mg and Si elements in the matrix and reduce the accumulation of impurities at grain boundaries.…”

“…Detailed preparation processes of Al–9Si–0.4Mg–0.1Cu alloy and Al–6Sr–7La can be obtained from previous works. [ 16,36 ] Specimen preparation processes were as follows: first, a certain amount of Al–9Si–0.4Mg–0.1Cu alloy was melted in a graphite crucible which was heated by a resistance furnace at 750 ± 1 °C; after the alloy was melted, the melt was kept for 20 min to ensure sufficient and uniform heating. After that, high‐purity argon gas (with purity of 99.99%) was applied to purify the melt with a constant speed of 0.1 L min −1 for 2 min, the slag was then removed, and an appropriate amount of Al–6Sr–7La composite refinement modifier was added.…”

“…Previously, Al–5Ti–B and Al–10Sr were applied to refine α‐Al and modify eutectic Si of Al–9Si–0.4Mg–0.1Cu alloy. [ 36 ] Though refining and modification effects are significant, the refining effect of Al–5Ti–B was weakened because of “Si poisoning” effect [ 19,29,36 ] and excessive Sr was needed because coarse Al 2 Si 2 Sr phase appeared, which consumed Sr atoms, resulting in excessive modification. [ 36 ] To avoid the earlier deficiencies, Al–6Sr–7La composite‐refining modifier was used and systematically heat treatment was applied in this work to optimize the mechanical properties of Al–9Si–0.4Mg–0.1Cu alloy.…”

“…[ 36 ] Though refining and modification effects are significant, the refining effect of Al–5Ti–B was weakened because of “Si poisoning” effect [ 19,29,36 ] and excessive Sr was needed because coarse Al 2 Si 2 Sr phase appeared, which consumed Sr atoms, resulting in excessive modification. [ 36 ] To avoid the earlier deficiencies, Al–6Sr–7La composite‐refining modifier was used and systematically heat treatment was applied in this work to optimize the mechanical properties of Al–9Si–0.4Mg–0.1Cu alloy. Optimal T6 heat treatment process parameters were obtained and its effect on microstructure and mechanical properties evolution was investigated.…”