Development of high strength Mg alloys by mechanical alloying

An attempt has been made to produce high strength Mg alloys by mechanical alloying with stearic acid as milling additive. The mechanically milled (MM) Mg powder of almost 100 % was recovered by adding stearic acid of 1.5 mass % or more. The optimum amount of the stearic acid was 2.5 mass %. The mechanically alloyed powder metallurgy (MA P/M) AZ91 alloy exhibited a Vickers hardness of 149 Hv, compressive yield strength of 704, MPa and plastic strain of 1.7 %. This alloy consisted of only hcp-Mg with a grain size of 100 to 200 nm. On the other hand, the MA P/M Mg97Zn1Y2 alloy exhibited a Vickers hardness of 118 Hv, compressive yield strength of 431 MPa and plastic strain of 4.7 %. This alloy consisted of Mg24Y5 and hcp-Mg with a grain size of 400 to 500 nm. Although the Vickers hardness of the MA P/M AZ91 alloy increased up to 162 Hv by a heat treatment, the heat treated alloy became very brittle.