| As a kind of Al-Si alloy, ADC12 aluminum alloy has good casting performance. It has been widely applied in the national economy. However, there are a lot of thick primary α-Al dendrite and long needle-like eutectic Si in the as-cast microstructure, resulting in the decrease of mechanical property. In addition, it will also introduce iron and other impurities in the process of smelting. Therefore, it is very necessary to take measure to control size and morphology of the phases in alloy to improve property. In this paper, the effect of(La+Yb) on ADC12 alloy was investigated by adding Al-5La-5Yb master alloy prepared by high-energy ultrasound intermittent.The results show that the addition of(La+Yb) obviously reduced the sizes of the primary α-Al phase and eutectic Si particles as well as harmful β-Al5 Fe Si phase. The secondary dendrite arm spacing, average diameter and average cell area of α-Al are refined significantly. The α-Al grain is arranged in neat rows and the orientation tends to be more consistent. The coarse needle or lath-shaped eutectic silicon refined into short rod or granular dispersed. In addition,(La+Yb) is helpful to increase the mechanical property of alloy. The tensile strength, elongation, elasticity modulus and hardness are both increased with the increase of RE, reaching the highest value when the addition is 0.6wt.%. In this case, the tensile strength, elongation, elasticity modulus and hardness are 275.40 Mpa, 4.92%, 73.09 GPa and 117 HV respectively, increased by 92.4%, 132.1%, 29.8%, 6.42% compared with unmodified alloy.And the fluidity of ADC12 alloy is improved obviously with the addition of(La+Yb). There is a quadratic function relationship between fluidity and the addition of RE. The optimal content is 0.52 wt.%, which has little to do the pouring temperature. The sensitivity of fluidity for pouring temperature is the highest when adding 0.6wt.% RE. In addition, the fluidity increases with the increase of pouring temperature. It appears to be a linear function of pouring temperature: Lf=7.943Tp-4750.783.The microstructures are improved observably after T6 heat treatment. The coarse needle or lath-shaped eutectic silicon refined into granular or circular particle, and the needle-like β-Al5 Fe Si is also refined, even changing into Chinese script or spherical α-Al8Fe2 Si. With T6 heat treatment, the mechanical properties are increased, and the plasticity is improved. Adding different content of(La+Yb), the properties are increased first and then decreased, reaching the highest value when the addition is 0.6wt.%. In this case, the tensile strength and elongation are 312.56 MPa and 3.86%, increased by 69.35% and 113.26% compared with unmodified alloy with T6.(La+Yb) and T6 heat treatment can significantly improve the wear resistance of ADC12 alloy. With the increase of(La+Yb), the weight wear rate and wear coefficient are increased first and then decreased, and the wear coefficient is stable. For casting alloy, when adding 0.6wt.%(La+Yb), the wear resistance is the best. In this case, the weight wear rate and wear coefficient are 4.42% and 0.30, decreased by 29.95% and 23.1% compared with unmodified alloy. After T6 heat treatment, the weight wear rate and wear coefficient are 0.43% and 0.26, decreased by 67.2% and 25.7% compared with T6 unmodified alloy, decreased by 90.3% and 33.3% compared with T6 alloy added 0.6wt.%(La+Yb). It shows up a kind of fatigue wear mechanism for casting unmodified alloy, but the T6 unmodified alloy is oxidation wear mechanism. However, they all show up a kind of abrasive wear mechanism for casting or T6 alloy with different(La+Yb) addition. |
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