论文总字数：35444字

摘 要

铸造Al-Si合金是目前工业中应用最广泛的铝合金之一，而砂型铸造Al-Si合金由于其成本低，适用范围广，研究其性能改善更具有工业应用价值。本课题主要通过应用La/B联合细化手段，在熔体中直接合成异质形核核心，从而对低冷速的砂型条件下的组织和性能进行调控，细化其晶粒尺寸，提高合金宏观力学性能。此外，考虑到组织变化对合金元素分布的影响，还对细化后合金的热处理工艺进行了初步探究，旨在探究固溶时效参数的变化，寻求一个适用于细化后Al-Si合金体系的热处理工艺。

本文以工业中最为常用的牌号合金ZL104合金和ZL101/ZL101A合金为主要研究对象，在低冷速砂型条件下进行良好变质、细化以及后续的热处理获得样品。通过OM、SEM等进行微观形貌观察其内部组织，用拉伸测试、硬度测试等手段进行表征其宏观性能，研究砂型铸造条件下Al-Si合金的组织和性能变化。

首先研究了La/B联合细化处理对砂型铸造板状铸件条件下的ZL104和ZL101A两类合金体系组织和性能的影响。结果表明晶粒细化对板状铸件样ZL104合金的组织细化效果明显；而由于ZL101A中Ti的存在夺取了有效B元素，ZL101A的组织细化效果较不明显。对应的宏观性能表现上，ZL104合金抗拉强度提高了19%，延伸率提高了31%，提升效果明显。而ZL101A合金抗拉强度提高了10%，延伸率提高了43%，性能有一定的提升。同时对通过国标标准砂型铸造得到的ZL104、ZL101A、ZL101合金进行了同样的La/B联合细化处理。微观形态上的结果与板状铸件类似，但宏观力学性能方面前两类合金体系都没有出现明显变化，而ZL101合金性能略有提高，原因主要是国标试样中较多的铸造缺陷影响了微观组织变化向宏观性能的体现。

通过硬度表征了合金固溶时效工艺在La/B联合细化前后的变化。主要探究了在固定的530℃固溶温度下细化对最佳固溶时间的影响，以及在175℃时效温度下细化对最佳时效时间的影响。结果表明，在板状铸件中细化使得ZL104合金和ZL101A合金达到固溶硬度峰值时间和时效硬度峰值时间发生提前。同时结合对共晶Si相长径比和平均尺寸的统计结果，可以认为细化后的板状铸件样品中两类合金最佳固溶和时效时间都有所提前，而对于ZL104这一效应更加明显。但在标准铸件中，La/B联合细化没有令热处理参数出现显著变化，分析认为标准铸件中存在的较多铸造缺陷依然是影响固溶和时效过程的重要原因，使得组织变化没有得到表现。

关键词：晶粒细化，砂型铸造，牌号合金，热处理参数

Abstract

Casting Al-Si alloy is one of the most widely used aluminum alloys in industry. So due to its low cost and wide application range, the study on the performance improvement of Al-Si alloy with sand mold casting has more practical significance. Therefore, in the subject, by applying the La/B joint refinement approach, the heterogeneous nucleated core is synthesized directly in the melt. We try to refine its grain size to adjust the structure and properties of the Al-Si alloy. Its aim is to improve the mechanical properties.

In addition, considering the influence of morphological changes on the distribution of internal elements, preliminary research on the heat treatment after refining was also conducted. The purpose is to research the changes of its solution aging parameters. And a heat treatment process suitable for refined Al-Si alloy system was also sought.

In this paper, ZL104 alloy and ZL101/ZL101A alloy, the most commonly used alloy in the industry, are taken as the main research object. And samples are obtained by good metamorphic, refining and heat treatment in sand mold. The microstructure of Al-Si alloy was observed by OM and SEM, and its macroscopic properties were characterized by tensile test and hardness test. The microstructure and properties of Al-Si alloy were studied under sand casting conditions.

Firstly, the effect of La/B refining treatment on microstructure and properties of ZL104 and ZL101A alloy systems in plate casting was studied. The results show that grain refinement has obvious effect on microstructure refinement of ZL104 alloy. However, due to the presence of Ti in ZL101A, the refinement effect of ZL101A is not obvious. In terms of mechanical performance, the tensile strength of ZL104 alloy increased by 19%., the elongation was increased by 31%. And ZL101A increased its tensile strength by 10%, elongation increased by 43% and performance improved slightly. The alloy ZL104, ZL101A and ZL101 obtained from standard sand mold casting were also refined by La/B. The micromorphological results are similar to those of plate casting. However, in terms of macroscopic mechanical properties, the first two alloy systems showed no significant changes. And ZL101 alloy has slightly improved properties. The main reason is that there are many casting defects in the national standard samples. The changes of solid solution aging process before and after refining were characterized by hardness. The influence of refining on the optimal solid solution time at the solid solution temperature of 530℃ was mainly investigated. And the effect of refining on the optimum aging time at 175℃. The results show that after the plate casting is refined, the peak time of solution hardness and aging hardness of ZL104 alloy and ZL101A alloy are advanced. Combined with the statistical results of the aspect ratio and average size of eutectic Si, it can be considered that both the optimal solution time and aging time are advanced, and the effect is more obvious for ZL104. In standard castings, the heat treatment parameters have no obvious change after refinement. The reason is presumed to be excessive casting defects in the castings.

KEY WORDS: Grain refinement, sand casting, brand alloy, heat treatment parameters

目 录

第一章 绪论 1

1.1引言 1

1.2 铸造Al-Si合金概述 1

1.3 砂型与金属型比较 2

1.4铸造Al-Si合金的变质 2

1.5 铸造Al-Si合金的细化 3

1.6 铸造Al-Si合金的热处理 4

1.7 稀土元素在铸造铝硅合金中的研究 5

1.8 研究内容与技术路线 6

第二章 实验过程与研究方法 8

2.1 实验原材料 8

2.2 合金熔制 8

2.3 热处理 11

2.3.1 固溶处理 11

2.3.2 时效处理 11

2.4 显微组织观察 11

2.4.1 光学显微镜(OM) 11

2.4.2 扫描电子显微镜(SEM) 11

2.5 力学性能测试 11

2.5.1 拉伸实验测试 11

2.5.2 硬度测试 12

第三章 实验结果与分析 13

3.1 铸态组织与性能 13

3.1.1 板状铸件组织与性能 13

3.1.2 标准铸件组织与性能 16

3.1.3 小结 22

3.2 热处理组织与性能 23

3.2.1 固溶处理工艺研究 23

3.2.2 时效处理工艺研究 27

3.3.3 小结 29

第四章 结论 31

参考文献 32

致 谢 35

第一章 绪论

1.1引言

铸造铝合金有着密度低，比强度高，耐腐蚀性能好等特点，从而在工业中得到了广泛应用，是汽车、造船、航空航天及其他制造行业的重要结构材料[1]。在汽车工业中使用铝合金，可以减轻自重，提高功率质量比，从而节约能源、提高效率^[2]。目前主要研究铝合金的熔炼和铸造工艺，如：铝合金净化、变质、细化、合金，这些工艺方法可以加强铸造合金的工艺性，从而提高合金的性能，生产出更优质的铸件^[1]。

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