The Research Of Microstructure And Properties Of RE AZ31 Alloys Prepared By Deoxidized RE Oxides

The present preparation of RE wrought magnesium alloy is using Mg-RE master alloy. It consumes rare earth resources in refined purification process. The pollution of fluoride and other toxic substances produced in the purification process is very serious. RE oxides are not only the natural forms of rare earth elements, but also the lead products of rare earth metal and Mg-RE master alloy preparation. It's easy to be purified and very cheap on market. Therefore, producing RE wrought magnesium alloy by deoxidized RE oxides can shorten the purification processe and master alloy production, cut down the generation of pollutants, and reduce the cost of the RE wrought magnesium alloy preparation.In this paper, AZ31 alloy was the matrix of study. The research of preparing RE-AZ31 alloy by rare earth oxides reduction was taken according to a pre-designed orthogonal scheme. The reduction rate of rare earth oxides was identified. This paper also have further discussion on the thermodynamics of RE oxides reduction reaction and the kinetics of RE oxide reduction rate influence factor. The microstructure mechanical properties, deformation property and the oxidation resistance of RE-AZ31 alloy that prepared by deoxidized RE oxide were studied and they are compared with that of RE-AZ31 produced by Mg-RE master alloys. The conclusion can be drawn as follows:?1? By preparing a series of RE-AZ31 alloy by single CeO₂, La₂O₃, and mixed RE oxides reduction, the reduction rate of single CeO₂ was up to 11.50%, single La₂O₃ reduction rate was up to 26.85%. The reduction rate of CeO₂ in the mixed RE oxides was 9.45%, and La₂O₃ reduction rate was 21.08%.?2? The main reduction reaction of single CeO₂ is: 2Mg+CeO₂=Ce+2MgO. There are three reactions in single La₂O₃ reduction: a. La₂O₃+ 3CaF₂ = 2LaF₃+ 3Ca O at first. Then reduction reaction: LaF₃+Mg=La+Mg F2; b. complexation reaction at first:?La₂O₃?+?F^-???LaOF?n^x-),then reduction reaction:?LaOF?n^x-)+[Al]?[La]+(AlF₆^3-)or?Al OF?; c. React first: La₂O₃+3Mg Cl₂=2LaCl₃+3MgO,then electrolytic reaction:LaCl₃??? La+Cl₂.The reduction process of mixed RE oxides according to the principle of CeO₂ and La₂O₃ respectively.?3? The analysis of optimal level of the orthogonal factors that affect the RE oxides reduction rate showed that: the addition of RE oxides, stirring time was proportional to the reduction rate of RE oxides. The best melting temperature was 710?. The main factor on the reduction rate of single CeO₂ and La₂O₃ was stirring time, the main effect factor on the reduction rate of mixed RE oxides was the addition of RE oxides. The regression equation was obtained by using the least square method. It was between the addition of RE oxides, stirring time and RE content of AZ31 alloy. Of CeO₂: ?_Ce=0.093x+0.067y-2.87; Of La₂O₃: ?_La=0.24x+0.068y-2.97; Of mixed RE oxdies: ?_Ce=0.084x+0.001y-0.341,and?_La=0.61x+0.041y-5.698. ?_Ce and ?_La are the Ce and Lacontent in AZ31 alloy, x is corresponding to the addition of RE oxides and y is stirring time.?4? The data showed that with the increasing of the RE content in AZ31, which prepared by deoxidized RE oxide, the grain size was refined. And the tensile strength, the rolling deformation and oxidation resistance were improved. However, when RE content increased to an extreme value, the grain size of alloy increases, and the properties start to decline. In comparison with the RE-AZ31 alloy prepared by Mg-RE master alloy, the microstructure and properties of RE-AZ31 alloy prepared by RE oxides were similar when RE contents in spcimens were the same. Therefore, the new method of preparation RE-AZ31 alloy can replace the Mg-RE master alloy method.