| Aluminum alloy A356 is widely used in industrial production because of its preferable castability,heat treatment properties,processability and fatigue properties,etc.The alloy is of choice of the aluminum wheels and pistons in auto industry.Based on the previous study of our group,this paper investigates a new type of master alloy A15Ti1B0.5RE,which was applied to the refinement of aluminum alloy A356 in production environment.The refining effect and mechanical properties of this master alloy is revealed by means of comparability experiments and modern analysis techniques such as OM,XRD,tensile testing,SEM,etc.The effects and mechanism of the refinement is explored in this paper.The main results are as follows.The aluminum alloy A356 is refined respectively by 3 kinds of A15TilB0.5RE master alloy(1#、2#、3#)prepared earlier in production environment.Due to the high-efficient purification technology for removing inclusions used in its preparation process,master alloy 3#has the best refining effect through some comparing experiments.Master alloy 3#has a better purity for it makes the refinement particles(TiAl3、TiB2)diffuse easier in aluminum melt,including the preferable size and the distribution of the refinement particles.The best technology processing parameters optimized by orthogonal experiment through range analysis for aluminum alloy A356 with master alloy 3#are:the treatment temperature for 730℃,the proper Ti content for 0.1%,standing time for 60min.Compared to pure A356,the alloy structure in orthogonal experiment group has been improved obviously.The average size of macro-grains of A356 in orthogonal experiment group is decreased,which of the A3 5 6 under the best scheme is only 0.40mm(pure A356 for 1.46mm).The distribution uniformity of eutectic silicon is improved obviously but the size.The refining effect of the self-made A15Ti1B0.5RE master alloy under productive condition is proved to be better than that of the commercial refiner A15Ti1B and the pure aluminum alloy A356.The average size of macro-grains of A356 with master alloy 3#is the smallest,which is 1/3 of the pure A356;also the average size of micro-grains is the smallest,which is 2/3 of the pure aluminum alloy A356.The reason is that the surface active element RE has a low solid solubility in aluminum melt.Element RE can easily get adsorption together between the grain boundary and the phase boundary of aluminum alloy,thus filling the defects of the grain surface,and hindering TiAl3 growing and the formation of needle or strip TiAl3 phase,which increases the nucleation rate on refinement nuclei.Moreover,element RE deceases the surface energy of aluminum melt,and increases the wetting angle of the refinement particles,which improves the spreading coefficient of TiB2 on α-Al matrix.Element RE also makes the size of grains smaller and the distribution of refinement particles better,which leads to decrease the tendency of TiB2 particles getting together.The comparing experiments also show that element RE has some action of purification and modification.The aluminum alloy A356 refined by master alloy 3#shows less casting defects,and the distribution uniformity of eutectic silicon in the alloy is improved obviously.The mechanical properties of the aluminum alloy A3 5 6 is related to casting grain structure,casting defects and the morphology of eutectic silicon.As the master alloy 3#has a better refining effect than commercial refiner,and it has purification and modification in some degree,the mechanical properties of the aluminum alloy A356 with master alloy 3#in general is better than that of the commercial refiner,which has the similar elongation percentage but much higher tensile strength. |
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