Improved age-hardening response and altered precipitation behavior of Al-5.2Mg-0.45Cu-2.0Zn (wt%) alloy with pre-aging treatment

• Pre-aging treatment improves the age-hardening response of the Al-5.2Mg-0.45Cu-2.0Zn alloy significantly.
• The microstructure of the alloy has been altered dramatically with pre-aging treatment.
• Detailed information about the compositions of the precipitates has been given.

In this research, pre-aging treatment has been performed on our newly developed Al-5.2Mg-0.45Cu-2.0Zn alloy. Results show that the age-hardening response of the alloy has been significantly improved with pre-aging treatment due to a modified precipitation microstructure. Without pre-aging treatment, the microstructure in peak aged condition consists of coarse lath-like T- Mg32(Al, Zn)49 phase and needle-like S-Al2MgCu phase. However, the microstructure of the alloy in peak aged condition with pre-aging treatment only consists of high density of finer and equiaxed T phase with the S phase disappeared. Though both kinds of T phases have the same body-centred cubic (BCC) Mg32(Al, Zn)49-type structure (Im3, a = 1.422 nm), they have big difference in composition. Schematic illustration of the precipitation behaviors in the alloy during aging at 180 °C with or without pre-aging treatment is made according to the analysis results.

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