Abstract
A high extrusion ratio of 166:1 was applied to commercial AZ61 alloy in one step with an extrusion speed of 2.1 m·min−1. The effects of DA (direct aging) treatment on the microstructure and tensile properties of extruded alloy were investigated. The extruded alloy exhibits fine DRXed grains and the average grain size is ~11 μm. After DA treatment at 170 °C, the tensile strength and 0.2% offset yield strength is enhanced from 314 to 336 MPa and from 169 to 191 MPa respectively, sacrificing elongation from 26.5% to 23.3%. The grain size and texture distribution of extruded AZ61 scarcely evolve during the post aging treatment. However, the enhanced strength in peak-aged alloy is mainly caused by the high-density elliptical Mg17Al12 precipitates distributing uniformly along the grain boundaries or within the grains, by precipitation and dispersion hardening. Furthermore, the nano-sized precipitates effectively inhibit grains from coarsening by triggering pinning effects along the grain boundaries at elevated temperature. As a result, the peak-aged alloy exhibits a better superplasticity of 306.5% compared with that of 231.8% of extruded sample. This work provides a practical one-step method for mass-producing Mg alloy sheets with excellent tensile strength and ductility compared with those fabricated by conventional extrusion methods.
Highlights
There have been numerous efforts to process fine-grained or nano-structured Mg alloys, with the aim of exhibiting specific mechanical properties, such as high strength and ductility
Fine and equiaxed grains distribute uniformly within the whole area, which indicates that dynamic recrystallization (DRX)
A high-ratio extrusion of 166:1 was successfully performed on the AZ61 alloy in one step without cracks extrusion for obtaining an alloy sheet less than 1 mm with a mass-producing of 2.1
Summary
There have been numerous efforts to process fine-grained or nano-structured Mg alloys, with the aim of exhibiting specific mechanical properties, such as high strength and ductility. Among various approaches in grain refinement, severe plastic deformation (SPD) methods have attracted considerable research interest. These SPD methods include high-pressure torsion (HPT) [1], equal channel angular extrusion (ECAE) or equal channel angular pressing (ECAP) [2,3], multiaxial forging (MAF) or multi-directional forging (MDF) [4,5], accumulative roll bonding (ARB) [6,7], as well as cyclic extrusion and compression (CEC) [8], etc. It has been confirmed that an intense deformation using one pass is more effective in obtaining ultrafine grains and high
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