混合稀土变质铝合金组织及性能研究

发布时间：2018-01-21 12:35

本文关键词： 混合稀土铝合金流动性 T6热处理摩擦磨损　出处：《南昌大学》2015年硕士论文　论文类型：学位论文

【摘要】：作为一种Al-Si合金,ADC12铝合金具有良好的铸造性能,在国民经济中得到了广泛应用。然而,其铸态显微组织含有大量粗大的初生α-Al枝晶以及长针状的共晶硅相,严重的降低了合金的性能。此外,在熔炼过程中也会引入较多的铁等杂质。因此,通过研究控制合金中这些相的大小和形貌来改善合金性能非常有必要。为此,本文通过向ADC12合金中添加高能间歇超声法制备的Al-5La-5Yb中间合金,探讨混合稀土(La+Yb)对铝合金组织及性能的影响。结果表明:混合稀土(La+Yb)的加入可以明显地细化组织中α-Al枝晶和共晶硅,改善有害β-Al5FeSi相。α-Al二次枝晶臂间距、平均直径和平均晶胞面积显著减小,晶粒排列整齐,取向趋于一致;粗大的针状或板条状共晶硅细化成弥散分布的短棒状或颗粒状;长针状或板条状β-Al5FeSi相形貌得到极大改善。当添加0.6wt.%的混合稀土时,变质效果最明显。混合稀土(La+Yb)可以极大地提高合金机械性。合金抗拉强度、延伸率、弹性模量和硬度均随着稀土加入量的增加而提高,当加入量为0.6wt.%时达到最高值,此时抗拉强度275.40 Mpa、延伸率4.92%、弹性模量73.09 GPa及硬度117 HV,相对基体分别提高了92.4%、132.1%、6.42%、29.8%。混合稀土(La+Yb)的加入可以显著改善ADC12铝合金的流动性。合金流动性与稀土添加量存在二次函数关系,最佳稀土添加量为0.52wt.%,而这个最佳值与浇注温度的关系不大。添加不同含量稀土时,加入量为0.6wt.%条件下ADC12铝合金流动性对浇注温度的敏感性最高。合金流动性随着浇注温度的升高而增加,存在近似Lf=7.943Tp-4750.783的直线型关系,可以适当提高合金浇注温度来改善流动性。经过T6热处理,合金组织得到显著改善,共晶硅由固溶处理前的长针状细化成小颗粒状或圆质点,长针状β-Al5FeSi相也变得短小细化,甚至转化成古汉字笔画状的α-Al8Fe2Si相。添加一定量的稀土,时效析出颗粒状Al2Cu强化相。T6热处理后,合金力学性能提高,塑性改善。添加不同含量的稀土,合金性能表现出先增大后减小的趋势。当添加0.6wt.%的混合稀土时,组织改善最佳,力学性能达最佳,塑性最好,抗拉强度与延伸率分别达到312.56 MPa、3.86%,相对热处理态基体分别提高了69.35%、113.26%。混合稀土(La+Yb)和热处理均可明显地改善ADC12合金的耐磨性,质量磨损率和摩擦系数大大下降。随着稀土添加量的增加,合金的质量磨损率和摩擦系数均表现为先减少而增加的趋势,摩擦系数波动稳定。当混合稀土添加量达0.6wt.%时,铸态合金耐磨性最好,质量磨损率和摩擦系数分别下降到4.42%和0.30,相对基体分别减少了29.95%和23.1%。T6热处理后,质量磨损率和摩擦系数分别下降到0.43%和0.26,相对热处理基体分别减少了67.2%和25.7%,相对铸态稀土合金分别下降了90.3%和33.3%。铸态基体合金表现出疲劳磨损的机制,T6热处理态基体则为氧化磨损机制;添加稀土后,铸态和T6态合金均表现出以磨粒磨损为主的磨损机制。
[Abstract]:As a kind of Al-Si alloy, ADC12 Aluminum Alloy has good casting properties, has been widely used in the national economy. However, the microstructures contain a large number of coarse primary alpha -Al dendrite and long acicular eutectic silicon phase, seriously reduce the performance of the alloy. In addition, iron and other impurities in the melting the process will also introduce more. Therefore, through the study of these phases in the alloy to control the size and morphology to improve the properties of the alloy is very necessary. Therefore, this article by adding Al-5La-5Yb master alloy prepared by intermittent high-energy ultrasound to ADC12 alloy, explore the mixed rare earth (La+Yb) and the influence on the performance of Aluminum Alloy organization. The results indicate that the mixed rare earth (La+Yb) could obviously refine alpha -Al dendrite and eutectic silicon, improve the harmful phase. Alpha -Al beta -Al5FeSi two dendrite arm spacing, average diameter and average cell area was significantly reduced, crystal The particle arranged to have the same orientation; acicular or lath coarse eutectic silicon refinement into dispersed rod like or granular; long needle or plate strip beta -Al5FeSi morphology has been greatly improved. When the mixed addition of rare earth 0.6wt.%, the most obvious modification effect. The mixed rare earth (La+Yb) can greatly improve the mechanical alloy. The tensile strength, elongation, elastic modulus and hardness were increased with increasing amount of rare earth, when adding to 0.6wt.% reached the highest value at 275.40 Mpa, tensile strength, elongation 4.92%, elastic modulus and hardness of 117 HV, 73.09 GPa, relative to the substrate were increased by 92.4%, 132.1%, 6.42%, 29.8%. mixed rare earth (La+Yb) liquidity could significantly improve the ADC12 Aluminum Alloy. There are quadratic function relationship between the fluidity of the alloy and rare earth content, the optimum adding amount of rare earth 0.52wt.%, and the best value and casting Little relation to temperature. Adding different content of rare earth, adding liquidity ADC12 Aluminum Alloy 0.6wt.% under the condition of pouring temperature was the highest. The fluidity of the alloy increases with the increase of the pouring temperature, there is a linear relationship between the Lf=7.943Tp-4750.783 type approximation, can improve the fluidity of increasing casting temperature of the alloy after T6 heat treatment. The microstructure of the alloy has been significantly improved, the eutectic silicon by solid solution refinement before long needle into small granular or circular particle, long needle like -Al5FeSi phase becomes short beta refinement, even transformed into a -Al8Fe2Si shape. The ancient Chinese characters strokes to add a certain amount of rare earth, precipitation granular Al2Cu.T6 phase after heat treatment. To improve the mechanical properties of the alloy, plastic improved. Adding different content of rare earth alloy, performance showed first increased and then decreased. When the mixed addition of rare earth 0.6wt.%, improve the organization The best mechanical properties was the best, the best plastic tensile strength and elongation were respectively 312.56 MPa, 3.86%, relative heat treatment state matrix were increased by 69.35%, 113.26%. rare earth (La+Yb) resistance and heat treatment can obviously improve the quality of ADC12 alloy, the wear rate and friction coefficient decreased greatly with increasing. The amount of rare earth alloy, the mass wear rate and friction coefficient were decreased and increased, the friction coefficient stability. When the mixed rare earth content was 0.6wt.%, the wear resistance of the cast alloy the best quality, the wear rate and friction coefficient are decreased by 4.42% and 0.30, relative to the matrix were reduced by 29.95% and 23.1%.T6 after heat treatment, the quality of the wear rate and friction coefficient are decreased by 0.43% and 0.26, the relative heat treatment matrix were reduced by 67.2% and 25.7%, relatively rare earth alloy as cast cast were decreased by 90.3% and 33.3%. The matrix alloy shows fatigue wear mechanism, and the T6 heat treated matrix is the mechanism of oxidation wear. After adding rare earth, the wear mechanism of the as cast and T6 alloy shows abrasive wear.

【学位授予单位】：南昌大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG146.21

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