Experimental Study On The Viscosity Of Mg-Al Alloys And Magnesium Matrix Composites

The viscosity of metal melts reflects the transport property of atoms.Viscosity is a measure of the friction among atoms.As the structural sensitive property.The viscosity of metal melts can build the connection between atomic structure and metal alloy properties.Therefore,the study of the viscosity of metal melts is of great significance.Mg-Al alloys are applied extensively in automobile,3C(refers to communication,computer,audiovisual),aerospace,defense and other fields due to their excellent properties,such as low specific gravity,high specific strength and specific rigidity,excellent shock absorption and machining performance.In this paper,the viscosities for melts of Mg-Al alloys with different compositions were systematically studied using a high-temperature viscometer.The research mainly focused on the temperature,compositions and the content of MgO on the viscosity of metal melts.In addition,the model to predict the viscosities has been discussed.In the present work,Yokoyama’s viscosity model and Eyring’s viscosity model were analyzed and modified.The experimental results showed that the viscosities of magnesium melts and MgAl melts all increase with decreasing temperature and fit well with Arrhenius equation.Under the same degree of superheated temperature,the viscosities of Mg-Al melts increase with the contents of Mg element in the Mg-Al alloys.In addition,it can be found that the viscosity of the Mg-3%Al melt has a significant increase relative to the pure Mg melt,while the viscosity slightly increases as the Al content continues to increase in the Mg-Al alloy.With the same superheated temperature 250 K,for example,the viscosity of Mg-3%Al is about 3.85 times that of Mg,but the viscosity of Mg-4%Al is about 1.01 times that of Mg-3%Al.As is well known,viscosity of liquid metals is a structural sensitive property at an atomic scale,so we can found that the liquid structure of Mg changes with the addition of Al element.When MgO particles were added to Mg-Al alloys,the viscosities also increase with decreasing temperature and fit well with Arrhenius equation.In addition,the viscosity increase with increasing the content of MgO.It is found that the viscosity of Mg-Al-1%MgO has a significant increase compared to the viscosity of Mg-Al,and the viscosity of MgO particulate reinforced magnesium matrix composites increases slightly upward as the content of MgO is increased.When the content of MgO is 1%,the order of the melt viscosity is Mg-7%Al>Mg-5%Al>Mg-3%Al>Mg,while 3%,the order is Mg>Mg-7%Al>Mg-5%Al>Mg-3%Al,this indicates that the effect of MgO particles on the viscosity of pure Mg and Mg-Al alloy melts is different.The modified Yokoyama model and the modified Eyring model have been obtained in this paper.The viscosities of Mg-Al alloys have been calculated with the modified model,and the results are consistent with the experimental data.Furthermore we found that,comparing the calculated values of the two modified models,in the low temperature region,the improved Eyring model can better follow the experimental results,but in the high temperature region,the improved Yokoyama model is better.