二元Al-Si合金力学行为与β-Si相形态间的相关性研究

发布时间：2018-03-23 12:17

本文选题：Al-Si合金　切入点：Si相形态　出处：《山东大学》2017年硕士论文

【摘要】：近共晶和过共晶Al-Si系合金以其铸造性能好、综合力学性能高、热膨胀系数低、导热性好等优点,成为制造活塞、汽缸等汽车零部件理想的轻量化材料。然而,粗大板块状的初晶β-Si相和针片状的共晶β-Si相(β-Si相以下简称为Si相)形态是降低其力学性能的主要因素。工业生产中常采用变质处理来改善Si相形态,从而提高拉伸性能。但目前Si相形态(包括Si相形貌、尺寸及分布等)对硬度、耐磨性等其它力学性能的影响规律尚缺乏系统研究。基于此,本文以近共晶Al-13Si和过共晶Al-25Si二元合金为主要研究对象,采用P、Sr变质处理Al-13Si合金分别获得过共晶/亚共晶组织特征形态;通过加P等熔体处理,使Al-25Si合金中初晶Si相呈不同尺寸及分布形态。研究了在成分一定的前提下,Si相形貌、尺寸及分布等变化时,Al-13Si和Al-25Si合金宏观硬度、拉伸性能以及摩擦磨损性能的变化规律;分析了硬度、耐磨性能等力学行为对Si相形态敏感性差异及其成因;研究了 Ca元素对P变质或细化的抑制作用机理,提出了一种高效环保的除Ca新工艺。本文主要研究工作如下:(1)近共晶Al-13Si合金Si相组织形貌及分布与力学行为的相关性研究发现,在室温条件下,当化学成分一定时,调控Si相形貌及分布并不能使Al-13Si合金的硬度发生明显变化,表明硬度对Si相形貌及分布不敏感。但Si相形态却显著影响拉伸性能和耐磨性能:合金经Sr变质处理后,Ω-Al基体与共晶Si相界面结合关系得到显著改善,拉伸强度达到205MPa,相比P变质处理提升23%左右,延伸率由1.03%提高至3.48%;摩擦磨损试验中合金的磨损量也较P变质的少,尤其是在高载荷(120N、150N)条件下,合金的耐磨性更好。与之相反,在高温(350℃)条件下,P变质后合金中Si相分布相对更均匀,变形更协调,合金拉伸强度更高,达到72MPa,延伸率为7.4%;摩擦系数变化更为平稳,耐磨性更佳。以上结果表明,合金拉伸性能和耐磨性均对Si相形貌及分布比较敏感。(2)过共晶Al-25Si合金初晶Si相尺寸与力学行为的相关性室温条件下,将A1-25Si合金初晶Si平均尺寸由200μm细化至15μm左右时,拉伸强度由99MPa提高至152MPa,比未细化时提高53%,延伸率由0.65%提高至0.94%;同样地,摩擦磨损试验中合金在高载荷条件下磨损量也明显减少,合金的耐磨性得到提升。但硬度值仍与细化前几乎保持一致,其它几组过共晶Al-Si合金的硬度值也反映了类似的规律。这说明Al-Si合金的室温硬度与Si相形貌、尺寸及分布变化无关,主要取决于Si的体积分数。高温(35℃)条件下,初晶Si相的细化同样有利于合金拉伸性能和耐磨性的提高:拉伸强度由66MPa提高至69MPa,延伸率由0.4%提升至2.7%;摩擦系数变得更加稳定。(3)杂质Ca对P变质或细化的抑制作用机理与除Ca新工艺系统研究了 Ca和P元素在Al-Si熔体中的相互作用,分析了 Ca添加量对P变质Al-13Si合金组织形态的影响,揭示了 Al-Si-Ca-P合金系中Ca的存在形态,发现其主要以Ca3P2形式存在,其次为Al2Si2Ca。利用Ca与P亲和力极强这一特性,提出了一种除Ca新工艺,即通过加入A1-P中间合金与铝合金熔体中的Ca反应使之以富钙化合物的形式除去。该工艺简便、高效、环保,可使合金中的Ca含量降至1Oppm以下。
[Abstract]:Near eutectic and hypereutectic Al-Si alloy with good casting properties, high mechanical properties, low thermal expansion coefficient, thermal conductivity and other advantages, become the manufacture of lightweight materials such as piston, cylinder auto parts ideal. However, the primary crystal beta -Si and bulky needle flake plate-like eutectic beta -Si phase (beta -Si hereinafter referred to as Si) form is a major factor in reducing its mechanical performance. Industrial production is often by modification to improve the morphology of Si phase, so as to improve the tensile properties. But the morphology of Si phase (including Si morphology, size and distribution) on hardness, wear resistance and other influence the mechanical properties are lack of systematic research. Based on this, this paper takes Al-13Si eutectic and hypereutectic Al-25Si alloy two as the main research object, using P, Sr modification of Al-13Si alloy were obtained in hypereutectic / hypoeutectic microstructure morphology; by adding P melt treatment, The primary Si phase in Al-25Si alloy with different size and distribution. On the premise of certain components, Si morphology, size and distribution changes of Al-13Si and Al-25Si alloy, hardness, tensile properties and friction performance variation; analysis of hardness, wear resistance and mechanical behavior of Si phase state the sensitivity difference and its causes; study the inhibition mechanism of Ca element on the P modification or refinement, put forward a kind of efficient environmental protection in addition to Ca new technology. The main research work are as follows: (1) study on the correlation between Al-13Si near eutectic alloy Si phase morphology and distribution and mechanical behavior found at room temperature and when a certain chemical composition, morphology and distribution regulation of Si does not make the hardness of Al-13Si alloy changed significantly, shows that the hardness is not sensitive to the morphology and distribution of Si. But the Si phase was significantly impact and tensile properties Abrasion resistance: Sr alloy after modification, has been improved significantly with -Al matrix and the eutectic Si phase interface, the tensile strength reached 205MPa, compared to P modification increase of around 23%, the elongation rate increased from 1.03% to 3.48%; the amount of wear of friction and wear test alloy than P becomes less, especially in high load conditions (120N, 150N), the better the wear resistance of the alloy. On the contrary, in the high temperature (350 DEG C) condition, P modification of Si in the alloy phase distribution is more uniform, the deformation coordination, the tensile strength is higher, up to 72MPa, the elongation is 7.4%; the friction coefficient changes stable, better wear resistance. The results above indicated that the tensile properties and wear resistance of the alloy are more sensitive to Si morphology and distribution. (2) at room temperature correlation of Hypereutectic Al-25Si alloy primary crystal size of Si phase and mechanical behavior of A1-25Si alloy under the average size of primary crystal Si by 200 m refinement To 15 m%, the tensile strength increased from 99MPa to 152MPa, 53% higher than that without the refinement, the elongation rate increased from 0.65% to 0.94%; similarly, friction and wear test alloy in high load conditions the wear volume was significantly reduced, the wear resistance of the alloy has been improved. But the hardness value is almost and refinement consistent with other groups of Hypereutectic Al-Si alloy hardness also reflects similar rules. This means that the Al-Si alloy at room temperature hardness and Si morphology, regardless of variations in size and distribution, mainly depends on the volume fraction of Si. The high temperature (35 DEG C) condition, the early phase refinement of crystal Si can also help the tensile properties and wear resistance of the alloy to improve the tensile strength increased from 66MPa to 69MPa, the elongation rate increased from 0.4% to 2.7%; the friction coefficient becomes more stable. (3) the mechanism of inhibition of P impurity Ca metamorphism or refinement with the exception of Ca new technology system of Ca and P elements in Al The interaction of -Si in the melt, analyzed the effect of Ca content on P modified Al-13Si alloy microstructure, reveals the existence form of Al-Si-Ca-P alloys Ca, which mainly exists in the form of Ca3P2, followed by Al2Si2Ca. using Ca and P strong affinity to this characteristic, put forward a kind of new technology in Ca. The Ca reaction by adding A1-P master alloy and Aluminum Alloy melt in the form of calcium rich compounds removed. The process is simple, efficient, environmentally friendly, can make the Ca content in the alloy is below 1Oppm.

【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG146.21

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