Tailoring the Microstructure and Mechanical Property of AZ80 Alloys by Multiple Twinning and Aging Precipitation

Abstract

AZ80 alloy is a relatively inexpensive age-hardenable Mg alloy. To improve its precipitation strengthening effect, the discontinuous precipitates generally nucleating from grain boundaries should be reduced. In this study, the authors applied strain-path change compression on a wrought AZ80 alloy to generate multiple {10-12} twins and then the pre-deformed alloy is subjected to aging at 180 C for different period. The effects of the pre-generated twins on precipitation behavior and hence the mechanical properties are investigated. It is found that multiple {10-12} twins are formed in the AZ80 alloy after two paths of compressions along the transverse and rolling directions. Consequently, continuous precipitation is largely promoted during the subsequent aging process. Moreover, the continuous precipitates preferred to form inside the {10-12} twin lamellae. Discontinuous precipitation is almost inhibited during aging at 180 C for 4-96 h in the sample containing many multiple twins. Compare to the directly peak-aged sample, the pre-twinned and subsequently peak-aged alloys generally exhibit greatly superior mechanical properties. The yield strength, ultimate strength, and elongation for tension along RD are 242 MPa, 476 MPa, and 19.4%, respectively. These excellent properties are attributed to the combined effects of grain refinement, texture weakening, and enhanced precipitate strengthening.

Regulating Precipitates by Simple Cold Deformations to Strengthen Mg Alloys: A Review

“…It can be used to promote the uniform precipitation, as reported by Li et al [37]. Moreover, it can also be used to generate non-homogeneous distribution of precipitates, as reported by Song et al [27], Wang et al [29] and Liu et al [11]. For example, torsion deformation induces gradient strain in rods, resulting in macroscopic non-uniform distribution of precipitation behavior [27].…”

“…For example, torsion deformation induces gradient strain in rods, resulting in macroscopic non-uniform distribution of precipitation behavior [27]. Transition of precipitation behavior relating to deformation twins can induce microscopic non-uniform distribution of precipitates [11,29]. Recently, the heterogeneous structure (e.g.…”

“…Thus, aging treatment usually only arouses static recovery, instead of static recrystallization, in pre-deformed Mg alloys. Deformation twins, deformation texture, and part of dislocations via pre-cold deformation can usually be remained after aging [27,28,29,30,31,32,33,34,35,36,37,38]. These microstructural changes can also generate a hardening or softening effect in yield strength.…”

“…Cold deformation before aging can introduce high density of crystal defects (e.g., dislocations, twins, stacking faults, et al) [20,21,22,23,24,25,26]. Such defects can efficiency accelerate diffusion rate of atoms and offer more nucleation sites for precipitates during aging, thus improving age-hardening effect [21,22,23,24,25,26,27,28,29,30,31,32]. Clearly, the cold deformation method can be a significant supplement to the above-mentioned methods.…”

“…In the previous studies, these alloy systems have also become the main research objects to study the influences of cold deformation on the precipitates. It is demonstrated that the cold deformation prior to aging in Mg alloys can effectively enhance the aging-hardening effect of various Mg alloys (including Mg-Al [27,28,29,30], Mg-Zn [31,32,33,34], and Mg-RE alloy systems [26,35,36,37,38]). Based on these alloy systems, the influences of cold deformation on precipitation features in Mg alloys were reviewed in detail in this review.…”