Abstract
This study evaluated the effect of UltraSonic Treatment (UST) on a range of Al–Mg alloys. Previous research was carried out on single magnesium compositions. However, the amount and type of the alloy addition are known to affect the grain size even under UST, and the aim of this study was to determine whether or not alloy composition plays a similar role in the case of Al–Mg alloys. By testing binary Al–Mg alloys cast under regular casting conditions and under the presence of an ultrasonic field, it was found that while the addition of Mg solute is important, the amount of solute has little effect when UST is applied. It was observed that the grain size was barely affected by extra solute additions in this condition. This is due to the application of UST during solidification, which resulted in a dramatic reduction in the size of the nucleation free zone thus promoting many more successful nucleation events. Acoustic streaming is proposed as the main cause of this reduction in grain size.
Highlights
Al–Mg alloys are known to have the highest strengths of all Al alloys without heat treatment, along with having good corrosion resistance and weld ability, resulting in the wide use of these alloys in industry
The asThe as-cast Al-5Mg alloy macrostructure shown in Figure 2a, has large coarse and irregular grains
This trend continues as the magnesium content increases to to 20%, though the rate at which the grain size decreases appears to become slower as additional Mg is
Summary
Al–Mg alloys are known to have the highest strengths of all Al alloys without heat treatment, along with having good corrosion resistance and weld ability, resulting in the wide use of these alloys in industry (especially naval sectors). These include the 5000 series of wrought alloys, and the 500 series of cast alloys [1]. When grain refinement has been applied, a correlation between the grain size reduction, and the number of casting defects has been observed These defects include: Porosity, macro-segregation, non-uniform properties, and hot and cold tearing [8,9]. There is a lack of information regarding the effects of alloy chemistry and grain refinement techniques on these
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