【作者】 葛良琦；

【导师】 颜银标；

【作者基本信息】 南京理工大学 ， 材料学， 2007， 硕士

【摘要】 高硅铝合金具有容重小、耐磨性好、铸造成型好、具有较好的尺寸稳定性等诸多优点，但因高硅铝合金中普遍存在粗大多角形的初生硅颗粒，严重割裂了基体，恶化了材料的性能，限制了其在工业上的广泛应用。目前主要通过变质处理、半固态技术、快速凝固以及电脉冲技术来对初生硅形态进行优化，但是这些手段不是效果不显著，就是技术条件复杂、成本过高，不适合进行大规模工业生产。本文系统研究了铸造工艺、变质工艺、扩散加热处理以及二次加热对初生硅颗粒形态的影响，同时还研究了通过不同处理工艺对初生硅尺寸、形态产生改变对材料力学性能、热膨胀性能以及磨损性能的影响。研究表明：变质处理能够很好地细化初尘硅，但是初生硅的形态仍然带有明显的尖角，在受到较大的外力作用时，不仅容易发生自身断裂，而且会容易与铝基体发生脱离：在扩散加热处理过程中，随着扩散温度的升高，保温时间的延长，能够很好的粒化、球化共晶硅组织，同时对初生硅颗粒的尖角处也有明显的钝化作用，但是保温时间过长对初生硅的粗化效应明显，反而不利于其形态的改善，而且过长时间的保温处理对初生硅形态的改善明显没有提高温度效果要好；二次加热效果对原始组织的形貌依赖性较强，对未扩散加热处理的组织进行二次加热，对初生硅尖角处有一定的钝化作用，但效果不是很明显；而对扩散加热处理后的组织进行二次加热可以发现，初生硅得到了明显球化。初生硅形态对组织性能的影响研究表明：随着初生硅的细化、球化，材料的塑性和强度都有明显的提高；而热膨胀系数与微观组织的形貌之间的关系不是很密切，更取决于材料中的硅含量：材料的磨损试验表明，在高硅铝合金进行磨损时，磨损量随着载荷的增加而增大，而磨损率随着载荷的增加而减小，摩擦系数与载荷的关系不是很明显：初生硅的细化、球化在一定程度上能够提高材料的耐磨损性能。本文通过整合优化这些简单、实用、易操作的技术手段，对初生硅颗粒实现了细化、球化，并取得了良好的效果，具有很好的实用价值。将试验结果应用到实际的生产过程中，不仅无需对生产设备进行改造，而且成本低廉，具有很好的经济意义和推动作用。更多还原

【Abstract】 There is a growing interest in hypereutectic aluminum-silicon alloys instead ofconventional materials due to low density, high wear resistance, favorable castability andlow thermal-expansion coefficient. However, the casting of hypereutectic Al-Si alloysalways present relatively coarser and brittle primary silicon particles with shape anglewhich degrade significantly both mechanical properties and mechinablity, and limit thefurther applications of these alloys. At present, several processing methods have beenapplied in fining and modifying the morphologies of primary silicon, such as addition ofmodifiers, semi-solid metal processing (SSM), rapid solidification, and pulse-electricdischarging processing, which is either not as efficient as expected, nor cannot be realizedin industry production due to sophisticated technology & facility, and high expense. Thisresearch has studied systematically on the influences of casting processing, modificationprocessing, diffusion heat treatment and reheating treatment on the size and morphology ofprimary silicon particles based on the prior work, and also investigated the mechanicalproperties, thermal expansivity and wear resistance of these processed materials.Several phenomenons can be observed in this research. Primary silicon particles canbe fined greatly with the increase addition of modifiers; nonetheless, such treatments havelimited influences on the morphologies change of silicon particles, whose sharp angleincrease the probability of both the crack of particle itself and the abruption betweensilicon and Al matrix. When processed by diffusion treatment, eutectic silicon particles canbe granulated and spheroidized obviously, while the sharp angle presenting in the primarysilicon will disappear with the increase of holding time & diffusion temperature. However,too longer holding time will lead to coursing of primary silicon particles, which will bedetrimental to the morphology of silicon particles; ohterwise, the effect of increasingholding time is not as obvious as increasing the diffusion temperature. The effect ofreheating treatment is dependent largely on the origin morphologies of particles, while thereheating temperature should be chosen just beyond the eutectic temperature. The sharpangle can be obtusen in the materials unprocessed by diffusion treatment, but the effect isnot very distinct, while the primary silicon within the materials processed by diffusiontreatment is greatly improved by reheating treatment.The properties test shows that, the plasticity and strength of hypereutectic Al-Si alloysare improved obviously with the refinement and spheroidization of primary silicon, whilethermal expansivity of materials has limited relationship with the morphology of primary silicon particles. Wear resistance test shows that the mass loss of all materials testedincreases with the increase of load while mass loss rate decreases with the increase of load;the wear resistance can be improved by the refinement and spheroidization of Si particles.In this work, several simple, but practical and easy-to-use technologies are utilizedand integrated to fine and spheroidize the primary silicon particles in Al-20%Si alloy, andthe processing effect of this route is very splendid. When utilizing this method in industryproduction, there are not any requirements on equipment modifications, and the rise in theexpense is very limited. As a result, this processing method is proved to be an effective andeconomic solution in modification of morphologies of primary silicon.更多还原