Effects of Mg Content on Hydrogen Content and Melt Quality of Al-Mg Alloys

• Main Authors: Ho Sung Jang, Ho Jeong Kang, Pilhwan Yoon, Gyuheun Lee, Jong Bae Jeon, Jin Young Park, Eok Soo Kim, Sunmi Shin
• Format: Article
• Language: English
• Published: MDPI AG 2019-11-01
• Series: Metals
• Subjects: aluminum alloy; melt quality; dissolved hydrogen; high temperature oxidation
• Online Access: https://www.mdpi.com/2075-4701/9/11/1235

In Al-Mg alloys with Mg content 0 &#8804; <i>X</i>_Mg &#8804; 6 wt. %, the effects of <i>X</i>_Mg 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 <i>X</i>_Mg and melt temperature <i>T</i>_Melt; these trends agree with theoretical calculations for hydrogen solubility. The tendency of melt quality vs <i>X</i>_Mg was similar in DI, BI, and porosity measurements, and the poorest melt quality was observed in the Al-4Mg alloy that had <i>X</i>_Mg = 4 wt. %, whereas the highest [H] was obtained in the Al-6Mg alloy melt that had <i>X</i>_Mg = 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 &#176;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.