Improving Tensile and Compressive Properties of an Extruded AZ91 Rod by the Combined Use of Torsion Deformation and Aging Treatment

Abstract

In this study, AZ91 magnesium alloy rods were used to investigate the effects of torsion deformation on microstructure and subsequent aging behavior. Extruded AZ91 rod has a uniform microstructure and typical fiber texture. Torsion deformation can generate a gradient microstructure on the cross-section of the rod. After torsion, from the center to the edge in the cross-section of the rod, both stored dislocations and area fraction of {10-12} twins gradually increase, and the basal pole of the texture tends to rotate in the ED direction. Direct aging usually generates coarse discontinuous precipitates and fine continuous precipitates simultaneously. Both twin structures and dislocations via torsion deformation can be effective microstructures for the nucleation of continuous precipitates during subsequent aging. Thus, aging after torsion can promote continuous precipitation and generate gradient precipitation characteristics. Both aging treatment and torsion deformation can reduce yield asymmetry, and torsion deformation enhances the aging hardening effect by promoting continuous precipitation. Therefore, combined use of torsion deformation and aging treatment can effectively enhance the yield strength and almost eliminate the yield asymmetry of the present extruded AZ91 rod. Finally, the relevant mechanisms are discussed.

A Novel Turning-Induced-Deformation Based Technique to Process Magnesium Alloys

“…Increased presence of continuous bands of precipitates was observed in the AZ91_DOC alloy compared to AZ91_AR. This suppressed the complete nucleation of new grains during extrusion in the deformed alloys, resulting in the presence of high amounts of worked grains, which was also expressed previously in [7].…”

“…This turning induced deformation approach was compared to the conventional cold deformation techniques such as torsion induced deformation, which was undertaken by [7], to understand the effectiveness of this approach. Figure 6 gives the mechanical properties of the same AZ91 alloy processed through this approach and the torsion induced deformation approach.…”

“…While this is a hot deformation technique, it was demonstrated that cold severe plastic deformation processes such as HPT (high pressure torsion) can render the AZ91 alloy superplastic [6]. Apart from these SPD techniques, effects of torsion deformation and ageing have also been studied [7] on age hardenable alloys such as the AZ91 alloy. It has been reported that this method was effective in reducing the yield asymmetry of the alloy, and deformation by torsion enhanced the effect of age-hardening that led to continuous precipitation, hence improving the mechanical properties of the alloy.…”

Simultaneously improving the corrosion resistance and strength of magnesium via low levels of Zn and Ge additions

“…Mg alloy AZ31 has the following properties YS= 229 MPa, total elongation = 15 %, AZ91 YS = 264 MPa, total elongation = 9 %, and WE43 YS= 237 MPa, total elongation = 16 %, as some examples [2,[77][78][79]. Indeed, the optimisation of alloying concentration in the Mg-Zn-…”

Cerium Addition Improved the Dry Sliding Wear Resistance of Surface Welding AZ91 Alloy

“…As the lightest-metal structural materials in practical applications, magnesium alloys have the advantages of a high specific stiffness and specific strength; they have been increasingly used in aerospace, military equipment, automobile manufacturing, and other fields [1,2,3,4]. During actual use, various local damage such as scratches, corrosion, wear, and tear on the surface of magnesium alloy structural parts or components are inevitable.…”