Effect of precipitation on strength and ductility in a Mg–Zn–Y alloy

Abstract

The effect of pre-ageing deformation on the size and distribution of β ′ 1 precipitates and subsequently on the resulting strength and ductility have been measured in a Mg-3.0at.%Zn-0.5at.%Y alloy. The alloy was extruded and then subjected to a T8 heat treatment comprised of a solution-treatment, cold-work and artificial ageing. Extrusion was used to introduce texture, ensuring that deformation occurred via slip rather than twinning. Samples were subjected to controlled uniaxial deformation and then isothermally aged to peak hardness. Precipitate length, diameter and number density were measured and evaluated in terms of the strength and ductility of the alloy. The nucleation of the β ′ 1 precipitates in peak-aged condition without pre-ageing deformation (i.e.T6 treatment) was poor, with only 0.5% volume fraction, compared to approximately 3.5% in T6 treated binary Mg-3.0at.%Zn alloy. The microstructure of the Mg-Zn-Y alloy was less refined, with larger diameter precipitates and lower β ′ 1 number densities compared to a binary Mg-3.0at.%Zn alloy. Deformation to 5% plastic strain increased the volume fraction of β ′ 1 precipitates to approximately 2.3% and refined the β ′ 1 precipitate length and diameter. The combination of these effects increased the yield strength after isothermal ageing from 217 MPa (0% cold-work) to 287 MPa (5% cold-work). The yield stress increased linearly with reciprocal interparticle spacing on the basal and prismatic planes and the alloy showed similar strengthening against basal slip to Mg-Zn. The elongation increased linearly with particle spacing. The ductility of Mg-Zn-Y alloys was similar to that of Mg-Zn for equivalently spaced particles.

Effect of precipitates on mechanical and damping properties of Mg–Zn–Y–Nd alloys

“…A dense dispersion of parallel rod-like precipitates and some lath-and sphere-shaped phases precipitated perpendicular to the end of the parallel ones can be observed in the Mg matrix. The rod-like phase is about 10 nm in width and 50 nm in length, which had been identified as MgZn 2 phase by Rosalie [16]. The rod-like form of MgZn 2 phase (referred to [0001]Mg) is typical precipitation for the aged condition in Mg-Zn based alloy.…”

Effects of heat treatment on microstructure evolution and mechanical properties of Mg-6Zn-1.4Y-0.6Zr alloy

“…With the result of EDS analyses shown in Table 1, the compositions of interior grain (region F) are mainly element Mg and a small amount of element Zn. According to relative investigations [13][14][15]22] , these dispersive particles ought to be nanoscale Mg-Zn binary precipitates during low temperature aging treatment, For the as-cast Mg-6Zn-1.4Y-0.6Zr alloy, the bulky net- …”

“…Meanwhile, the I-phase decomposed gradually with the formation of thermally stable W-phase. Generally, W-phase is not considered as an effective strengthening phase because of its limited structural symmetry and weak adhesive force with α-Mg matrix [14] .…”

“…Compared with thermal deformation, heat treatment can obtain superior mechanical properties with simple processes and low cost. Hence, precipitation hardening is an attractive way to improve the strength of Mg-Zn-Y-Zr alloys [14][15][16][17] . Zn and Y elements exhibit relatively high solubility at elevated temperature and limited solubility at low…”

Precipitation behavior of an ultra-fine grained Mg–Zn alloy processed by high-pressure torsion

“…In the previous studies, all of the work were performed to study the precipitation behavior in as-cast [17], extruded [18] and ECAPed [19] samples, in all of which the grain size is in micron-scale range [20]. However, little work has been done to study the ageing and precipitation behaviors in the Mg-based alloys with nano-scale UFG structure processed by SPD.…”