Achieving high strength in ZK60 based Mg alloy with a low RE content though numerous precipitates

Abstract

This research aims to explore the possibility of a high-strength Mg alloy with a low RE content. The Sm element was added to the Mg-6Zn-0.5Zr-3Nd alloy. The corresponding microstructures and performance evolution were systemically investigated, and the strengthening mechanisms were quantified. It was indicated that Sm addition not only enhanced the precipitation process but also changed the precipitates. The Mg-Zn phases disappeared, and the original Nd₃Zn₁₁ phases were replaced by the (Nd,Sm)₃Zn₁₁ phases after Sm addition. Extrusion further enhanced the precipitation process. Both micron-scale precipitates distributed along the grain boundaries and nanoscale precipitates distributed within the grains can be observed in the as-extruded alloys. The Sm addition inhibited the DRX process but had no influence on the grain orientation, and all alloys displayed an incomplete DRX structure. Sm15 exhibited the best mechanical properties, with an ultimate tensile strength of 430 MPa, which can be attributed to the combined effects of strong texture strengthening and Orowan strengthening. Although Sm20 displayed a better Orowan strengthening effect than Sm15 because of the higher volume fractions of precipitates, its mechanical properties decreased because of weakening of grain boundary strengthening and texture strengthening.