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Development of novel grain refiners for AZ91D magnesium alloys and their effect on hot tearing

University of British Columbia

Wider implementation of ultralight magnesium (Mg) alloys in engineering applications can be achieved if the mechanical properties of mass produced as-cast alloys can be further enhanced. Grain refinement of aluminum alloys has supported such initiatives over the past few decades; however, a potent and cost-effective grain refiner for common aluminum containing Mg alloys remains elusive. Further, the effect of grain refinement on common casting defects, such as hot tearing, in Mg alloys remains unclear. In this work, several novel grain refiners were produced via the powder metallurgical process known as spark plasma sintering (SPS). The novel grain refiners were used to treat AZ91D Mg alloy and a grain size reduction of ~75 - 85% was achieved, along with improved dispersion of secondary phases and modified eutectics. Such microstructure modifications during solidification resulted in the elimination of hot tearing in castings where hot tearing was typically observed. The SPS’ed refiners were also observed to outperform a common commercially available grain refiner. Many advanced analysis techniques that were implemented in this research provided further understanding of the mechanism behind the effectiveness of the SPS’ed grain refiners. Additionally, the casting experiments were completed using a unique force contraction mold, providing quantitative data during solidification. Furthermore, the results of microstructure evolution, solidification kinetics and forces, as well as in-situ solidification analysis via neutron diffraction, was related to the grain refinement and hot tearing of AZ91D Mg alloy.

Text

2019-05-01

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/70021

Mechanical Engineering

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/4.0/