Inclusion Measurement and Identification in Mg-Based Alloys: Application of the Brightimeter Technique

The present investigations were carried out on experimentally prepared AM50A and AZ91D alloys. The main thrust was the application of the Brightimeter technique in quantifying the concentration of the inclusions in these alloys. The results show that the Brightimeter indices are low when the amount of oxides, i.e., MgO, Al2O3, Al2MgO4 is high. Reducing the oxide concentration increases the Brightimeter readings (indices). It is concluded that the Brightimeter apparatus is an effective technique in determining the metal cleanliness in terms of detecting and measuring the inclusion content. Its sensitivity increases with the increase in the amount of inclusions. At low levels of inclusion concentration, there is a noticeable fluctuation in readings of the Brightimeter. The main parameter to be considered is the melting and solidification process. It is recommended that the Brightimeter readings (indices) should be coupled with metallographic examination. The main inclusions are magnesium oxides (MgO), magnesium hydroxides (Mg(OH)x), aluminum oxides (Al2O3), spinel (a mixture of MgO + Al2O3). In some cases, pure metals such as iron (Fe) and aluminum (Al) were also observed along with their oxides, i.e., FeO and Fe2O3. The use of flux as a protective agent may cause the presence of other types of inclusions such as K, Na and Ca. The quantity of oxides depends to a large extent on the inclusions initially present in the as-received alloy. Recycled alloys were found to contain the maximum amount of inclusions.