Effect of Y, Sr, and Nd additions on the microstructure and microfracture mechanism of squeeze-cast AZ91-X magnesium alloys

Abstract

This study aims to investigate the effects of Y, Sr, and Nd additions on the microstructure and microfracture mechanism of the four squeeze-cast magnesium alloys based on the commercial AZ91 alloy. Microstructural observation, in situ fracture tests, and fractographic observation were conducted on the alloys to clarify the microfracture process. Microstructural analyses indicated that grain refinement could be achieved by small additions of alloying elements, although the discontinuously precipitated Mg 17 Al 12 phases still existed on grain boundaries. From in situ fracture observation of an AZ91-Sr alloy, it was seen that coarse needle-shaped compound particles and Mg 17 Al 12 phases located on the grain boundary provided easy intergranular fracture sites under low stress intensity factor levels, resulting in the drop in toughness. On the other hand, the AZ91-Y and AZ91-Nd alloys showed improved fracture toughness, since deformation and fracture paths proceeded into grains rather than to grain boundaries, as the planar slip bands and twinnings actively developed inside the grains. These findings suggested, on the basis of the well-developed planar slip bands and twinnings, that the small addition of Y or Nd was very effective in improving fracture toughness.

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

“…Similar results were reported by other researchers. [17,18,19] However, these experiments were performed at a constant cooling rate, and the grain refinement mechanism of Sr is not clear. Recently, the authors [20] reported that Sr also had a significant grain-refinement effect in wrought magnesium alloy AZ31.…”

Fracture toughness in a rolled AZ31 magnesium alloy

“…One of the distinction methods is the investigation of fracture toughness. There are some reports about the values of fracture toughness in magnesium alloys [6][7][8][9]. The value of fracture toughness in a wrought magnesium alloy has been generally reported to be higher than that in a cast magnesium alloy.…”

Hot Cracking of Metal Inert Gas Arc Welded Magnesium Alloy AZ91D

“…[1][2][3][4] Among the commercial magnesium alloys, AZ91D is widely used. 5) Besides the development of new alloy types, manufacturing techniques such as welding and joining play an important role in exploiting the new fields of applications.…”