Microstructure And Mechanical Properties Of Micro-alloyed Recycled ADC12 Aluminum Alloy

This paper mainly studies the effect of trace elements on the microstructure and properties of recycled ADC12 aluminum alloy,and quantitatively analyzes the modified matrix structure to reveal the mechanism of microalloying.In order to further improve the performance of the secondary aluminum alloy,the alloy composition with the best as-cast performance is selected for heat treatment,and the orthogonal design is used to optimize the process parameters.The research shows that:The addition of rare earth La,Ce and Y has obvious refining effect on the α-Al secondary dendrite spacing and eutectic Si phase of the alloy.As the content increases,the refinement effect is more obvious.When La,Ce and Y were added,the α-Al secondary dendrite spacing decreased from 32.2 μm to 23.1 μm,and the eutectic Si phase length decreased from 43.1 μm to 5.5 μm,which were refined by 28.8% and 76.8%,respectively.Moreover,it has a certain refining effect on the size of the needlelike Fe-rich phase,which is reduced to 30.4 μm compared with 32.1 μm without adding Cr,and the decrease range is about 5.36%.The length drops to 20.24 μm,which is 36.95% thinner than before adding.The mechanical properties test of the alloy shows that the tensile strength,elongation and hardness of the alloy have been significantly improved due to the modification of the eutectic Si phase and the acicular Fe-rich phase.The tensile strength,elongation and hardness after adding La,Ce,Y and Cr are 192.1 Mpa,1.43% and 93.6 HV,respectively,which are 22.7%,72.3% and 25% higher than those of the unmodified recycled ADC12 aluminum alloy,respectively.,the fracture mode of the alloy also changes from brittle fracture to quasi-cleavage fracture.Compared with the recycled ADC12 aluminum alloy without heat treatment,the eutectic Si phase is further spheroidized and the size is further refined after heat treatment.alloy structure.At the same time,the fragmentation of the needle-like Ferich phase was also observed,and the formation of the complex phase of Al Si Fe Cu was also found at 530 °C.Due to the slow diffusion of Fe in the Al matrix,even if the heat treatment temperature is increased,the size of the needle-like Fe-rich phase still does not decrease much,about 10.9%,and the fragmentation of the rare earth phase is not observed.The tensile strength,plasticity and microhardness of the alloy were tested respectively,and the orthogonal results showed that the factors that had the greatest influence on the three were aging time,aging temperature and aging time,respectively.Corresponding heat treatment process parameters.In terms of mechanical properties of the alloy,taking the tensile strength(267.1 MPa)of the alloy measured in Test 3 as an example,it is about 39.1% higher than that without heat treatment,and the effect is obvious.After heat treatment,the strength of the alloy can be greatly improved without sacrificing too much plasticity of the recycled ADC12 aluminum alloy.The fracture of the alloy after heat treatment was analyzed,and the results showed that with the optimization of the heat treatment process,the fracture mode of the microalloyed regenerated ADC12 aluminum alloy changed from pure brittle fracture to ductile fracture and intergranular fracture.The change trend of elongation properties is more consistent.This study is expected to provide theoretical support for the recycling of recycled aluminum,and promote the maintenance and even upgrade of recycled aluminum products.