Abstract
In Al-Mg alloys with Mg content 0 ≤ XMg ≤ 6 wt. %, the effects of XMg on dissolved hydrogen content ([H]) and melt quality were investigated. [H] was measured using the Closed-Loop Recirculation method, and the melt quality was quantified using the density index (DI), bifilm index (BI), and porosity measurement. [H] in the molten alloys increased with increasing XMg and melt temperature TMelt; these trends agree with theoretical calculations for hydrogen solubility. The tendency of melt quality vs XMg was similar in DI, BI, and porosity measurements, and the poorest melt quality was observed in the Al-4Mg alloy that had XMg = 4 wt. %, whereas the highest [H] was obtained in the Al-6Mg alloy melt that had XMg = 6 wt. % Mg. During thermogravimetric/differential thermal analysis, rapid oxidation occurred in the Al-4Mg alloy melt during the holding time between 45 and 60 min at 800 °C., i.e., just before the molten metal was cast. The inferior melt quality of Al-4Mg alloy may have been caused by high-temperature oxidation.
Highlights
IntroductionHigh-strength aluminum (Al) alloys can be used to reduce the weight of vehicles [1,2]
High-strength aluminum (Al) alloys can be used to reduce the weight of vehicles [1,2].Non-heat-treated Al-Mg sheet alloys have excellent strength and high formability, so they are used as a structural material for inner panels
The bifilm index (BI) and density index (DI) melt are both quality-measurement methods that consider the effects of inclusions and dissolved hydrogen content ([H])
Summary
High-strength aluminum (Al) alloys can be used to reduce the weight of vehicles [1,2]. The Mg addition decreases the formation of protective oxide films on the melts, and these changes lead to increase in the numbers of pores and inclusions in the melt, with consequent degradation in melt quality [5]. The main internal defects in molten aluminum alloys include hydrogen and inclusions. Semiquantitative, and quantitative tests are available to estimate molten metal cleanliness; combinations of these measurements have been used for complete evaluation of melt quality. Representative methods of measuring melt quality include: (1) Closed-Loop Recirculation (CLR) [9], (2) Reduced pressure tests (RPT) [10], (3) K-mold [7],. The BI and DI melt are both quality-measurement methods that consider the effects of inclusions and dissolved hydrogen content ([H]).
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