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 0.4wt.%, 0.6wt.% and 0.8wt.%. Iron and Be were added in the form of Al–25%Fe and Al–5%Be master alloys, respectively, to obtain Fe levels of 0.09wt.%, 0.2wt.% and 0.6wt.% and a Be level of 0.05wt.%. The beryllium–iron phase is observed to occur in script-like form inside primary α-Al dendrites and close to Fe phases. Increasing both Mg and Fe levels in the alloy increases the amount of the π-Al8FeMg3Si6 phase formed. In solution heat-treated alloys, the β-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 π-phase is observed to dissolve and/or transform into a cluster of very fine β-Al5FeSi phase platelets. Beryllium addition results in a nodular form of the β-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 12h. 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. [Display omitted] •Enhancement of the alloy tensile properties due to fragmentation of Fe-based intermetallics during solution heat treatment•Significant improvement in the alloy tensile properties with addition of Sr plus Be•Beneficial effects of the use of Q-charts in determining the alloy performance•Influence of Fe-based intermetallics and heat treatment on the fracture mechanism