Effects of Cu, Mg, and Sr additions on the mechanical properties and machinability of near-eutectic Al-11%S casting alloys

This study was conducted with the intention of investigating a new experimental alloy, namely the 396 alloy which belongs to the Al-Si near-eutectic cast alloy group and contains about 11%Si. In the light of the above, the main purpose of the work is to report on the changes observed in the mechanical and/or machinability criteria resulting from the effects of the presence of two levels of Cu, namely 2.25% and 3.5%; and of the effects of two levels of Mg, namely 0.3 and 0.6%. In addition to the preceding, the effects of Mg-free alloys and Sr-modification on these same alloys were also investigated. The results demonstrate that the increase in the levels of Cu and/or Mg in the 396-T6 alloy has a detrimental effect on drill life. Such an effect may be attributed to the formation of large amounts of the coarse blocklike Al ₂Cu phase, together with the formation of thick plates of the Al-Si-Cu-Mg phase. The Mg-free experimental alloy displays the lowest cutting force and moment in addition to producing the highest number of holes in the alloys studied. A comparison of the non-modified alloy and the Sr-modified alloy (containing the same level of Mg and Cu additions) in terms of the number of holes drilled, reveals that the morphology of Si particles has a noticeable effect in governing the tool life of near-eutectic Al-Si alloys.