| A356 aluminum alloy has excellent casting,welding performance,low density,and high specific strength,so that it could be widely used in automotive,high-speed rail,aerospace and other fields.In this paper,the Al-Ti-B-Sr,a metamorphic agent suitable for A356 aluminum alloy,was prepared and fabricated by microalloying for the refined and modification to ?-Al phase and eutectic Si phase of A356 aluminum alloy.The effects of the amount of alloying elements on the microstructure and mechanical properties of A356 alloy and the mechanism of heat treatment on the microstructure and mechanical properties of composite after modification were studied.1.The effects of refining and degassing processes on the microstructure and mechanical properties of A356 alloy were studied.The results show that the impurity and gas in the alloy can be effectively eliminated by the argon degassing after the alloy is removed by the refining agent,the density of the alloy is improved,and the mechanical properties of the alloy are improved.The tensile strength and elongation of the alloy were 180 MPa and 5.7% when the flow rate of Ar gas was 10 ml / min and the aeration time was 5min,respectively.2.The microstructure and the mechanical properties of A356 alloy were researched with the different additions of Al-10 Sr master alloy.The results show that the modification of the eutectic Si phase in the alloy can be improved by the modification of the Sr element,and the transformation from coarse needle-like and slab-like to fine granular and rod-like is observed,and the mechanical properties of the alloy are improved remarkably.The tensile strength and elongation of the alloy are204 MPa,10.4% and 62.4HB,respectively.And the tensile strength of the alloy isobviously improved compared with that of the non-metamorphic alloy.3.The microstructure and the mechanical properties of A356 alloy were researched with the different additions of Al-5Ti-B master alloy.The results show that the Al-5Ti-B master alloy has a remarkable effect on the refinement of ?-Al dendrites in the A356 alloy,and the mechanical properties of the alloy are improved obviously.When the addition amount of Al-5Ti-B master alloy is 0.3wt.%,the alloy grains are the most uniform and the length-diameter ratio about 1.72.At the same time,the mechanical properties of the alloys are the best,the tensile strength and elongation are210 MPa,9.5%,compared with the A356 without refinement,the mechanical properties of the alloy has been significantly improved.4.In this paper,according to the researching on the the microstructure and the mechanical properties of A356 alloy with the Al-10 Sr and Al-5Ti-B master alloy,the four different contents and conditions of the Al-Ti-B-Sr master alloy were prepared,including the Al-5Ti-B-10 Sr,Al-5Ti-B-5Sr,Al-2.5Ti-0.5B-5Sr and the Al-3.5Ti-0.7B-3Sr.The effect of Al-Ti-B-Sr on the microstructure and properties of A356 alloy was studied.The results show that the microstructure of A356 alloy and the ?-Al dendrites are refined when the addition of Al-2.5Ti-0.5B-5Sr reaches0.6wt.%,the eutectic silicon phase changed from coarse needle-like and slab-like to fine rounded granularity and small bulk.The tensile strength and elongation of the alloy were 194 MPa and 19.1%,respectively.The microstructures and mechanical properties of the A356 alloy with the Al-5Ti-B,Al-10 Sr,Al-5Ti-B and Al-10 Sr,and Al-2.5Ti-0.5B-5Sr,the result shows that the addition of 0.6wt.% Al-2.5Ti-0.5B-5Sr was the best,and it could refine the ?-Al dendrites and eutectic Si phases at the same time.The mechanical properties of the alloys were improved obviously,and the elongation was improved greatly,which fully reflects the high efficiency of Al-Ti-B-Sr.A356 aluminum alloy is a heat treatable cast aluminum alloy,through a certain heat treatment process can improve the mechanical properties of the alloy greatly.Therefore,the influence of T6 heat treatment parameters on the microstructure and mechanical properties of A356 after refined and modified were discussed.The resultsshow that the optimum T6 heat treatment process is 540 ? × 6h + 155 ? × 6h,the eutectic silicon phase has the smallest size of 2.6?m and the roundness of 0.8,which is nearly round and granular but a few blocks.Meanwhile,the mechanical properties of the alloy was best,and the tensile strength and elongation of the alloy were 269 MPa and 19.6%.Compared with no heat-treatment alloy,the tensile strength and elongation were increased by 49.4% and 243.9%,respectively. |
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