Abstract
AAddition of Al – Be master alloy to a Mg – Zr alloy reduces melt oxidation, however, it has a detrimental grain coarsening effect that is believed to be caused by an unknown interaction of Be with the Zr nucleant particles. However, this study found that Al is the major cause of grain coarsening. By analysis of intermetallic phases and chemical analysis for solute Zr, it was revealed that Al reacts with the undissolved α – Zr particles forming Zr – Al intermetallic phases and reducing the amount of solute Zr both of which lead to a decrease in the grain refinement efficiency of the master alloy. Despite this negative effect of Al on grain refinement, application of ultrasonic treatment produces significant grain refinement of the Mg – Zr – Al – Be alloy demonstrating the potential for developing ignition-proof and grain refined Mg alloys.
Highlights
Ultrasonic treatment (UST) applied during alloy solidification produces excellent grain refinement which is necessary to achieve improved mechanical properties of the alloys (StJohn et al, 2005, 2013; Eskin, 2014, 2017)
The use of an Al—Be master alloy is the standard practice of adding Be to commercial Mg alloys and for permanent mold castings with the maximum addition being limited to 0.01% Be (Zeng et al, 2001b; Czerwinski, 2014)
The best refinement conditions for the Mg— 1Zr—AlBe alloy can be expressed as UST-S > UST-L > as cast
Summary
Ultrasonic treatment (UST) applied during alloy solidification produces excellent grain refinement which is necessary to achieve improved mechanical properties of the alloys (StJohn et al, 2005, 2013; Eskin, 2014, 2017). This attractive feature of UST facilitates opportunities to explore new alloy systems for which an appropriate grain refiner is unavailable (Nagasivamuni et al, 2018). In carbon inoculated commercial Mg—Al alloys the interaction of Fe or Mn with C is reported to cause poisoning of grain refinement (Easton et al, 2006; Du et al, 2010) while the application of UST results in excellent grain refinement (Ramirez et al, 2008; Nimityongskul et al, 2010)
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