Effect of strontium on the microstructure, mechanical properties, and fracture behavior of AZ31 magnesium alloy

Abstract

The effect of strontium (Sr) on the microstructure, mechanical properties, and fracture behavior of AZ31 magnesium alloy and its sensitivity to cooling rate are investigated. Three phases-blocky-shaped Mg 17 Al 12 , acicular Mg 20 Al 20 Mn 5 Sr, and insular Mg 16 (Al,Zn) 2 Sr-are identified in the Sr-containing AZ31 alloys. With increasing cooling rate, the blocky-shaped Mg 17 Al 12 phase increases, the acicular Mg 20 Al 20 Mn 5 Sr phase diminishes, and the insular Mg 16 (Al,Zn) 2 Sr phase is refined and granulated. The study suggests that the grain size decreases with increasing cooling rate for a given composition. However, the grain size decreases first, then increases, and finally decreases again with increasing Sr for a given cooling rate. The yield strength ( y ) of AZ31 magnesium alloy can be improved by grain refinement and expressed as y ϭ 35.88 ϩ 279.13d Ϫ1/2 according to the Hall-Petch relationship. The elongation increases when Sr is added up to 0.01 pct and then decreases with increasing Sr addition. Grain refinement changes the fracture behavior from quasicleavage failure for the original AZ31 alloy to mixed features of quasicleavage and microvoid coalescence fracture.

Effects of Cooling Rate and Solute Content on the Grain Refinement of Mg-Gd-Y Alloys by Aluminum

“…Other than nucleants and solute, solidification conditions also significantly affect the grain size of cast components. [12][13][14][15] Moreover, the solidification conditions can also affect the morphology of intermetallic particles. [16,17] Magnesium alloys containing rare earth (RE) elements usually exhibit excellent mechanical properties.…”

“…However, the grains became coarsened when the cooling rate was increased to 16.5 and 22.6 K/s (Figures 2(c) and (d)), contrary to general observations that grains become refined with increasing cooling rate. [7,13,14] The optical micrographs of Mg-10Gd-2Y alloys with 1 pct Al addition are shown in Figure 3. The grains were equiaxed with an irregular shape at a cooling rate of 1.4 K/s (Figure 3(a)).…”

Mechanical Properties and Microstructure of Magnesium-Aluminum Based Alloys Containing Strontium

“…Similar result was obtained by Yuan et al 17) In addition, Nam et al 18) also found that the modification efficiency of Sr to Mg 2 Si phase in the microstructure of containing-Si magnesium alloys was better than that of Sb element. The effect of strontium on the microstructure of AZ31 magnesium alloy was investigated by Zeng et al 19) The phase diagrams of Sr-containing magnesium alloys are important base for investigation on the compounds of Mg-Sr based alloys. However, only limited work has been done on the phase diagrams of magnesium alloys containing Sr. 7,20,21) In 2003, Koray et al 20) calculated the liquidus projection of the ternary Mg-Al-Sr system, and the calculated phase diagram exhibited substantial disagreement with the experimental data.…”

“…The research results obtained by Lee et al 22) showed that the grain size of magnesium and its alloys with low Al content could be reduced by adding minor Sr, but the refinement efficiency for magnesium alloys with high Al content was not obvious. In addition, Zeng et al 19) reported that the refinement efficiency of Sr to AZ31 magnesium alloy was affected by cooling rate. For a given Sr addition, the grain size of AZ31 alloy decreased with the increase of cooing rate (Fig.…”

“…9 Effects of cooling rate on the grain size of AZ31 + xSr alloys. 19) different states had different effects on the grain refinement of magnesium alloys (Fig. 10).…”