Effects of Zn additions on the microstructure and hardness of Mg–9Al–6Sn alloy

• A maximum hardness value of 103 HV is achieved by the addition of 3 wt.% Zn in the Mg-9Al-6Sn alloy.
• The addition of Zn decreases the solid solubility of Sn in the Mg-9Al-6Sn alloy.
• The formation of fine Mg2Sn particles leads to a significant hardness increment in the as-quenched condition.

The effects of Zn additions on the age hardening response and microstructure of Mg–9Al–6Sn (wt.%) alloy have been investigated. It is found that the Zn additions can remarkably increase the alloy hardness in the as-quenched condition. The peak hardness value of the Mg–9Al–6Sn alloy increases from 90 ± 0.87 HV to 103 ± 3.83 HV, when the Zn addition is 3 wt.%, which is the highest among the magnesium casting alloys that are free of rare-earth elements. The enhanced hardness in the Mg–9Al–6Sn–3Zn alloy is attributable to an increased volume fraction of smaller Mg2Sn particles in the solution-treated condition and the formation of [0001]Mg Mg17Al12 rods and Mg21(Zn, Al)17 precipitates in the peak-aged condition.