| ADC12(Al-Si-Cu)alloy is widely used in the automotive industry,3C products,military ships,aerospace,etc.,due to its good casting properties.However,China still lags behind the international advanced level in the development of high-quality hypoeutectic ADC12 alloy castings and its forming technology.This has seriously affected the ability of domestic foundry companies to accept orders for high-quality Al-Si-Cu alloy products,and caused huge losses to the company in terms of economy and brand establishment.Therefore,the development of high-quality die-cast aluminum-silicon-copper alloys and the research on the forming mechanism have great practical significance and academic value.This article aims to give full play to the modified alloying effect of different alloying elements in the aluminum-silicon-copper alloy at ultra-low micro content.Various methods clarify the influence mechanism and strengthening mechanism of the joint action of different alloying elements on the growth behavior of the eutectic silicon phase in the high strength and toughness Al-SiCu alloy.The development of high-cost and high-quality aluminum alloy materials provides unique solutions.On the basis of a large number of previous experiments,using ultra-low microalloying and uniform experimental design techniques and methods,the effect of ultra-low rare earth element and strontium mixed microalloying process on the microstructure and mechanical properties of ADC12 alloy was studied.Realize the controllable preparation of high-strength and toughness die-casting ADC12 alloy.The mechanical properties of the as-cast ADC12 alloy show that the modification effect is the best when the addition amount of Sr is 0.04 wt.%,the ultimate tensile strength is246 MPa,and the elongation is 2.4%.After determining the optimal addition amount of Sr,the influence of the modification process parameters such as the addition amount of rare earth,the addition temperature and the holding time on the tensile strength and elongation of ADC12 alloy was studied.When the addition amount of Sc is 0.0225 wt.%,the modification temperature is 760?,the modification time is 35 min,the casting temperature is 625?,and the mold is the modification process condition of the copper mold,the Sr+Sc modified alloy has the best comprehensive mechanics.The ultimate tensile strength of the alloy is 292.95 MPa,and the elongation is 2.87%,which is 33.15% and 108% higher than that of the unmodified ADC12 alloy.We used SEM,EDS,OM,Rockwell hardness tester to study in detail the effect of Sr+Sc modifier on the microstructure and mechanical properties of as-cast and die-cast ADC12 alloys.In the modified as-cast ADC12 alloy,the eutectic Si changes from coarse needles to very fine particles,the ?-Al phase changes from typical dendrites to ovals,and the size is further reduced;the ?-Fe phase is mostly transformed It is fibrous;all the copper-rich phases are transformed into tiny dots.A similar transformation also exists in the modified die-cast ADC12 alloy.Due to the faster cooling rate of the diecast alloy,the internal structure transformation is more thorough and the size is smaller.In terms of mechanical properties: die-cast ADC12-Sr-Sc alloy has the characteristics of high strength and toughness.Its ultimate tensile strength and elongation are 341 MPa and 5.68%,respectively,which are 35% and 373% higher than that of the unmodified die-cast ADC12 base alloy.This high-strength ADC12 alloy is only prepared by adding0.06 wt.% Sr+Sc(0.04 wt.% Sr+0.0225 wt.%)modifier.We use APT to study the distribution of ultra-low microalloying elements in eutectic Si and ?-Al,reveal the existence of trace elements in the alloy,and explore the composition and distribution of nanoparticles(or clusters)formed in the alloy.The high-efficiency modification mechanism and strengthening behavior of eutectic silicon in the high-strength and tough ADC12 alloy with ultra-low content of trace elements are explained.The results show that in the mixed modified eutectic Si,Sr is adsorbed on a specific growth interface of eutectic Si in the form of Si-Al-Sr nanoclusters,and Sc is adsorbed on eutectic Si in the form of Sc atom-rich aggregates.At the other growth interface,the combined action of the two metamorphic elements blocked most of the dominant growth directions of eutectic Si,thereby significantly inhibiting the growth rate of eutectic Si.In terms of strengthening behavior,the strengthening phase particles in the ?-Al matrix can effectively improve the ultimate tensile strength and yield strength of the alloy by hindering the movement of dislocations.At the same time,the improvement of the structure in the modified alloy can not only increase the strength of the alloy,but also greatly increase the alloy's ability to accommodate dislocations.These two effects are superimposed together to make the die-cast ADC12-Sr-Sc alloy a kind of high strength and toughness alloy. |
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