【作者】 张强；

【导师】 龙剑平； 李程；

【作者基本信息】 成都理工大学 ， 材料工程， 2015， 硕士

【摘要】 稀土元素能显著改变铸造Al-Si-Mg合金的组织形貌和力学性能,在国防、交通、电线电缆、建筑型材中有广泛的应用前景。稀土元素大致以单质元素、中间合金以及氧化物等方式引入,其引入方式会对铝合金改性产生影响,但相关研究报道较少。铸造Al-Si-Mg合金一般需要经过时效处理以改善其力学性能,铸造Al-Si-Mg合金的时效特性研究已经比较充分,但有关稀土改性铸造Al-Si-Mg合金的时效特性研究相关报道也较少。本论文研究了稀土镧引入方式对铝合金的微观组织及力学性能的影响,并对稀土改性铸造Al-Si-Mg合金的时效特性进行了系统深入的研究。稀土元素的引入方式对合金的改性效果存在明显差异。以氧化物的方式引入稀土镧,稀土的引入能对ZL101合金起到一定的细化作用,但对合金并无变质效果；添加量较少时,能一定程度强化基体合金,当稀土氧化物含量大于0.6%时,合金强度反而直线下降；以Al-La中间合金的方式引入稀土镧,能显著细化和变质ZL101合金,且合金的硬度也得到显著提高。XRD分析结果表明,La203的引入并未改变ZL101合金的物相；以Al-La合金的方式引入稀土后,生成了新的化合物(Al8Si8MgLa2),新形成的化合物聚集在共晶硅和初晶铝的界面上,引起合金性能的下降。合金经固溶、时效后,共晶硅的形貌变化较大,长条状的共晶硅几乎全部变为球状和颗粒状。以Al-Ce合金的方式引入稀土Ce对ZL104合金具有明显的细化效果,当添加量为0.6%时,其细化效果最明显,且硬度明显提高,但当稀土Ce添加量过多时,反而会降低合金的铸态及时效硬度。特别是Al-Ce合金添加量为1.6%时,时效过程中其析出相的析出比原始合金反而提前,但改性后合金的热焓高于ZL104合金的热焓。稀土元素La、Ce的引入能显著提高Al-Si-Mg合金的时效硬化作用,当Al-La合金的含量为0.5%时其强化作用最佳,Al-Ce合金的含量为0.6%时强化作用最佳。稀土元素La、Ce的引入对铸造Al-Si-Mg合 金的峰值时效时间具有延迟作用,并且随着稀土元素La、Ce引入量增多,其峰值时效时间延迟的效果越明显。稀土元素的引入并未改变合金的析出序列,但稀土元素的添加对于合金主要的析出强化相(β"、β’)和稳定相(Mg2Si)的析出具有延迟作用。随着稀土La的添加量增多,对ZL101合金的稳定相的析出抑制作用越明显；随着稀土元素Ce引入量的增多,对ZL104合金的析出相(β"、β’、Mg2Si)抑制作用越明显。温度对合金的时效硬化行为有显著的影响,时效温度越高,达到时效峰值的时间越短。更多还原

【Abstract】 The addition of rare earth can significantly change the morphology and mechanical properties of casting Al-Si-Mg alloy, it has a broad application prospect in the defense, transportation, building materials, wire and cable.Rare earth elements generally introduced into the alloy by elemental, intermediate alloy and oxide form. The introduction will have effect on aluminum alloy, but few related research has been reported. Al-Si-Mg Cast alloy generally improve the mechanical properties by the way of aging treatment, related research has been more fully reported, but the research about aging characteristics of the rare earth modified Al-Si-Mg alloy cast is less. This paper studied the change about microstructure and mechanical properties modified by different introduction, and the aging characteristics of rare earth modified Al-Si-Mg cast alloy.There are obvious different effect modified by different introduction way. Introduce oxide, the rare earth have a few refinement effect for the ZL101 alloy, But deterioration is not obvious, small rare earth can certain extent strengthen the matrix alloy. When the content of rare earth oxides is greater than 0.6%, the strength of the alloy is straight down; Al-La Alloy Can refine and deterioration the ZL101 alloy, and the hardness of the alloy has also been significantly improved.XRD result suggest that the addition of La2O3 has not changed phase in ZL101 alloy. Al-La intermediate alloy produce Al8Si8MgLa2,The new compound accumulation in the interface between the eutectic silicon and aluminum liquids, it decrease the mechanical properties of the alloy. The morphology of eutectic silicon have changed after solide solution and aging treatment, the strip morphology of the eutectic silicon almost become spherical and granular after solide solution and aging treatment.By the way of introducing the La、Ce intermediate alloy has distinct refining effect. The most distinct refinement occurs when amount of rare earth is 0.6% and the hardness increased most significantly at the same time. It reduce the hardness of cast alloy and aging alloy while adding too much, Especially 1.6%,On the study of precipitated sequence, the exothermic peak appears in advance compared to the original alloy. But the enthalpy is higher than Z1104 ally.The introducing ways of Al-Ce、Al-La alloy have obvious effect on the strength of Al-Si-Mg alloy. The strengthening effect is best when the introduction of Al-La alloy is 0.5%, The strengthening effect is best when the introduction of Al-Ce alloy is 0.6%.rare earth elements La, Ce delay the peak aging time on the casting of Al-Si-Mg alloy, with the introduction of rare earth elements increased, the peak aging time delay effect is more obvious.The introduction of rare earth alloy did not change the precipitation sequence. Al-Re alloy delay the release strengthening phase(β"、β’)and stable phase(Mg2Si) of alloy. The more adding of Al-Re alloy, the more obvious of inhibitory effect.The temperature has a significant impact on hardening behavior of alloy. With the increasing of aging temperature, peaking aging time is short.更多还原