Comparative study of the metallurgical quality, microstructure and mechanical properties of primary and secondary AlSi7Mg(Fe)aluminium alloys

The use of secondary aluminium is increasingly being promoted in the automotive industry for environmental reasons.

The purpose of this work is to demonstrate that, it is possible to obtain a recycled AlSi7Mg(Fe) aluminium alloy with as good metallurgical quality as that of a primary AlSi7Mg alloy when an adequate melt treatment is applied.

The melt treatment applied consisted of deoxidation, degassing and skimming in accordance with the detailed procedure described in this article. The metallurgical qualities of one primary and three secondary alloys have been assessed by thermal analysis, density index test, macro inclusion test before and after melt treatment.

The thermal analysis allows to compare the variables of the solidification cooling curve (Al primary temperature and its undercooling; Al-Si eutectic temperature and its predictive modification rate); Density Index test is used to evaluate the hydrogen gas content in the melt; Macro inclusions test is used for melt cleanliness evaluation.

Finally, the metallurgical analysis and mechanical properties of the different samples were made to show the feasibility of manufacturing aluminium components by using 100% secondary aluminium alloy returns through the gravity die casting technology.