Abstract
Aluminum Alloy AA-7034 is a high strength wrought alloy with reasonable ductility containing 10–12 wt% Zn, 2–3 wt% Mg, and 0.8–1.2 wt% Cu. This work investigates the effect of varying the concentration of Zn (10–12 wt%) and Cu (0.8–1 wt%) on the solutionizing and aging behavior of squeeze cast AA-7034 samples. The same behaviors were investigated when Mg content was increased beyond 3 wt%. The solutionizing heat treatment dissolved much of the macroscopic second phases present in the as-cast AA-7034 alloys, but a significant amount of second phases remain after solutionizing in alloys with >3 wt% Mg. The behaviors of the various Al-Zn-Mg-Cu alloys are compared to squeeze cast Al-A206 casting alloy heat-treated to the T7 condition. All Al-Zn-Mg-Cu alloys obtained higher hardness values than those obtained by Al-A206-T7.
Highlights
The quaternary Al-Zn-Mg-Cu wrought alloys offer advantageous physical and mechanical properties making them desirable for aerospace, automotive and defense applications
High Zn content alloys typically exhibit high hardness and high strength; they have been shown to have a higher content of residual T phase that is not dissolved upon solutionizing which can lead to stress concentrations [7]
Though the hardness is higher in the Al-A206 sample poured at 983.15 K (710 °C) due to smaller grain size than the Al-A206 sample poured at 1173.15 K (900 °C), it is clear that the solutionizing and aging heat treatments applied to the squeeze cast Al-Zn-Mg-Cu samples resulted in hardness values considerably higher than Al-A206 in the T7 condition
Summary
The quaternary Al-Zn-Mg-Cu wrought alloys offer advantageous physical and mechanical properties making them desirable for aerospace, automotive and defense applications. Metals 2014, 4 strength through various precipitates that are obtained through heat treatment Due to their high alloy content, they are generally considered to have poor cast-ability, suffering from porosity, hot tear defects, poor fluidity and inhomogeneous cast microstructure [1]. The amount and type of precipitates formed as well as the residual solid solution concentration can have a profound effect on the mechanical properties of these alloys. This work investigates the effect of composition on the solutionizing and artificial aging behavior of (1) variations of Cu and Zn that are within the limits of the AA-7034 specification and (2) variations of Mg beyond the limit of the AA-7034 specification
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