Effect of Alloy Composition, Solidification Rate, Porosity Level, Grain Refining and Modification on the Performance of Aluminum-Based Alloys

This study investigated the influence of various melt treatments with strontium, boron as well as gas removal through injecting high purity argon, on the hardness and tensile properties of 220, 356 and 357 cast alloys. The castings were produced using a permanent mold (ASTM-B-108, secondary dendrite arm spacing (SDAS) ~ 26 µm) preheated at 450 °C. The results were compared with findings obtained from parts made using an industrial lost foam technique (SDAS ~ 68 µm) to examine the influence of casting process and solidification rate. During aging, precipitation of ultra-fine Mg₂Si particles takes place during aging, which enhances the mechanical properties of the alloy; the extent of strengthening depends on the alloy’s Mg content, since Mg₂Si volume fraction increases with Mg level. Thus, the study confirms that proper melt treatments are the major parameters to be considered to improve the mechanical properties of Al-7%Si-(0.5-0.6)%Mg- and Al-2%Cu-0.45%Mg-based alloys. Independent of mold type, gains in mechanical properties due to a refined microstructure and reduced porosity.