Effect of intermetallics on the microstructure and tensile properties of aluminum based alloys: Role of Sr, Mg and Be addition

The present work was performed on B357 alloy containing Mg, Fe, Be and Sr. The molten metal was cast in a metallic mold (ASTM B-108). The Mg level of the alloy was increased by adding pure Mg to the alloy melts to obtain Mg levels of 0.4 wt.%, 0.6 wt.% and 0.8 Mg. Iron and Be were added in the form of A1-25%Fe and Al-5%Be master alloys, respectively, to obtain Fe levels of 0.09 wt.%, 0.2 wt.% and 0.6 wt.% and a Be level of 0.05 wt.%. The beryllium-iron phase is observed to occur in script-like form inside primary et-Al dendrites and close to Fe phases. Increasing both Mg and Fe levels in the alloy increases the amount of the pi-Al8FeMg3Si6 phase formed. In solution heat-treated alloys, the beta-phase platelets are observed to undergo changes in their morphology due to the dissolution, thinning, necking, and fragmentation of these platelets with an increase in solutionizing time. The pi-phase is observed to dissolve and/or transform into a cluster of very fine beta-AlsFeSi phase platelets. Beryllium addition results in a nodular form of the beta-phase which decreases the harmful effects of these particles on the mechanical properties. Quality index values increase with an increase in solution heat treatment time, from 5 to 12 h. Raising the Mg content leads to an increase in tensile parameters. Raising the Fe levels, however, leads to a drastic decrease in properties. For the same levels of Fe and/or Mg, Be and Sr help to improve the alloy mechanical properties. This is more prominent in alloys containing low levels of Fe with high levels of Mg. (C) 2015 Elsevier Ltd. All rights reserved.