Research And Preparation Of Sr Metamorphic Al₃Ti/ADC12 Aluminum Matrix Composites

The development of material is an important component for human civilization,As society develops, people are increasingly demanding for high performance materials. Aluminum alloy as one of then extremely widespread non-ferrous materials for its low density, good form ability, high strength, easy recovery and utilization are favored by people. ADC12 aluminum has been widely used for its superior performance. However, when the Si content exceeds 6%, coarse α-Al phase and a long needle-Si phase has seriously reduced the performance of material. The study found, Some phase（ Al₃ Ti, Al2O3 particles, etc.） prepared by in-situ reinforced reaction can improve the organization of Al-Si alloy and improve the mechanical properties of the alloy. At the same time, add a small amount of modifier（eg: Na, K,RE, Sr and other elements） in the Al-Si based alloy can not only achieve good refining effect modification, and also has a purifying melt degassing effect. Sr as an ideal efficient modifier, can change the sheet eutectic Si phase to a fine fibrous structure. Therefore, this paper is based on Al-Ti reaction system, in situ reaction way to prepare Al₃ Ti/ADC12 Aluminum Matrix Composites and to include Al-10 Sr master alloys in it, Prepared in situ Al₃ Ti/ADC12 aluminum matrixc omposites with different Sr contents, discuss the effect of Sr addition amount to the microstructure and properties of Al₃ Ti/ADC12 aluminum matrix composites. The main contents and results are as follows:In Al-Ti reaction system, the cryolite（Na3AlF6）and titanium powder（Ti）mixed powder was added in ADC12 aluminum alloy to prepare in-situ Al₃ Ti/ADC12 aluminum matrix composites, Al₃ Ti phase was massive aggregate distribution, size about 65μm. When 0.25wt% Sr content was added to Al₃ Ti/ADC12 aluminum matrix composite, modification effect ideal. α-Al grains completely refined, mainly in spherical or ellipsoidal shape, grain size is about 15μm, eutectic Si phase not only becomes granular, and evenly dispersed, Al₃ Ti phase from massive and totally into granular spread out. Meanwhile, the addition of Sr modifier makes the mechanical properties of the material raised, when adding 0.25wt% Sr, the material has bettermechanical properties, tensile strength of material reaches 281.74 MPa, elongation of2.56%, compared with Al₃ Ti/ADC12 aluminum matrix composites without Sr content were increased by 36.89%, 58.02%. The fracture morphology of material were analyzed, while not adding Sr, on the fracture surface substantially no dimple appear, only a few large shallow dimples fracture flush and there are some bright chevron pattern, fracture mode obvious cleavage fracture, when adding 0.25wt% Sr content, almost have not see the fracture and brittle cleavage plane flat area, tearing ridge becomes fine and uniform, increase in the number of dimples and more evenly distributed, the majority of dimples are small and deep, as intergranular fracture mode fracture, which will considerably improve the mechanical properties of the material.For the study of Sr metamorphic Al₃ Ti/ADC12 aluminum matrix composite wear resistance: its wear resistance is inversely proportional to the hardness of the material, with the increase of Sr content, the hardness of the material firstly increase and then decrease, reaching a peak at 0.25wt% Sr add content. under the same load to explore the influence of Sr Addition on wear rate and friction coefficient, obtained that 0.25wt% Sr amount of composite have better wear resistance, at 80 N load due to the increase wear debris between the pin and the disc, instantaneous fluctuations in the friction coefficient becomes large. With the same Sr content to explore the different loads on the wear rate and friction coefficient, wear rate and friction coefficient increases with larger load; Different Sr contents Al₃ Ti/ADC12 matrix composites under different loads exhibited wear mechanisms are not the same, in10-40 N load, wear form of material were mainly abrasive wear and oxidation wear, at80 N load wear form of material were mainly delamination wear and plastic deformation. observe wear debris SEM image of 0.25wt% Sr content Al₃ Ti/ADC12 aluminum matrix composite with 20 N, 80 N load, under 20 N load, debris with particulate, form a strand presented to verify the presence of abrasive wear; under80 N load, wear debris are not only have some small hard particles, but also some grinding sheet, indicating the form of delamination wear.For the study of Sr metamorphic Al₃ Ti/ADC12 aluminum matrix hrat treatment:designed to Sr addition amount（A）, solution temperature（B）, time of solution（C）, aging time（D）are the reference variable make four factors- and four levelsorthogonal test program. Analysis the influence of Sr addition amount on material heat treatment, when no modifier Sr added, the number of si phase quantity is small per unit area and dimensions sizes is different, add Modifier Sr to 0.25wt%, eutectic si phase distributed uniformly and roundness improved, evenly distributed, when sr content is too much will make heat-treated tissue poisoned, generating a small amount of needle like inter-metal compound, which would make the material mechanical properties decline; Add Modifier Sr also effectively improved tissue defects in materials, refinement of pores; When the solution temperature is low, it can cause iron-rich phase hard to dissolve in the α-Al phase,the solution temperature too high will produce over-burning phenomenon, the best solution temperature is 520 ℃;when solution time is 6h, α-Al phase is large, eutectic silicon phase is short stick,Fe-rich phase is bone-shaped, increasing solution time, further refinement of eutectic Si phase, Fe-rich phase to needle like; Make SEM and line scan of the organization after heat treatment, it can concluded that copper-rich phase is uniformly dissolved in the matrix after sufficiently heat treatment, and Fe element content is lower in the grain, higher in grain boundaries, indicating that the iron-rich phase is still concentrated in the grain boundaries.