In-situ reactions in hybrid aluminum alloy composites during incorporating silica sand in aluminum alloy melts

In order to gain a better understanding of the reactions and strengthening behavior in cast aluminum alloy/silica composites synthesized by stir mixing, experiments were conducted to incorporate low cost foundry silica sand into aluminum composites with the use of Mg as a wetting agent. SEM and XRD results show the conversion of SiO 2 to MgAl 2 O 4 and some Al 2 O 3 with an accompanying increase in matrix Si content. A three-stage reaction mechanism proposed to account for these changes indicates that properties can be controlled by controlling the base Alloy/SiO 2 /Mg chemistry and reaction times. Experimental data on changes of composite density with increasing reaction time and SiO 2 content support the three-stage reaction model. The change in mechanical properties with composition and time is also described.