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摘要 本課題主要介紹了加Si后的ZA38鋅鋁合金的微觀組織及力學(xué)性能，研究了Si含量變化對ZA38鋅鋁合金的微觀組織及力學(xué)性能的影響，同時研究了Si含量的變化對鋅鋁合金熱疲勞性能的影響。本課題主要通過光學(xué)顯微鏡、萬能拉伸試驗(yàn)機(jī)、SEM、自約束全自動冷熱疲勞試驗(yàn)機(jī)等儀器對加Si的ZA38鋅鋁合金組織及熱疲勞性能進(jìn)行系統(tǒng)地研究。

    實(shí)驗(yàn)結(jié)果表明：ZA38合金由初生α相、α相間的（α+η）共析體和ε相組成。ZA38合金中加入不同含量的Si元素后，合金的組織形態(tài)有較大差異，Si元素的加入量為0.55%時，合金組織細(xì)化程度最大，由未添加Si元素時的粗大樹枝晶轉(zhuǎn)化為細(xì)小等軸晶，且分布均勻。

ZA38合金中Si含量達(dá)到0.55%時，抗拉強(qiáng)度達(dá)到最大值405Mpa，比不加Si時提高了2.5%，延伸率達(dá)到最大值4.33%，增加了18.6%。隨著Si含量的增加，ZA38合金的硬度隨之增大。但合金中的Si含量過高時，合金組織中大塊Si相明顯增多，會割裂基體，從而造成應(yīng)力集中，使其力學(xué)性能變差。

ZA38合金的熱疲勞裂紋的擴(kuò)展程度主要受兩方面的影響：一是合金的強(qiáng)度和塑性；二是合金中的Si相的分布情況。當(dāng)ZA38合金中Si元素含量為0.55%時，Si相尺寸適中，均勻分布在基體上，合金組織得到最大細(xì)化，在熱循環(huán)應(yīng)力作用時，會阻礙位錯運(yùn)動，使合金的熱疲勞抗性得到提升。當(dāng)Si的含量過高時，初生Si相粗化，以塊狀和長條狀分布在基體上，合金的強(qiáng)度和塑性都變差，熱疲勞抗力大大降低。ZA38合金熱疲勞性能由好到壞依次為：0.55%Si，0.3%Si，0.8%Si，0%Si，1.3%Si，1.05%Si。

關(guān)鍵詞：ZA38；顯微組織；合金力學(xué)性能；熱疲勞性能

 

Abstract  This subject mainly introduces the microstructure and mechanical properties of the ZA38 zinc aluminium alloy through addition Si, and study The effect of Si content on the microstructure and mechanical properties of ZA38 Zn-Al alloy and The effect of Si content on the thermal fatigue properties of Zn-Al alloy, This subject mainly through optical microscope, universal tensile testing machine, SEM, self constraint automatic cold and hot fatigue testing machine and other equipment to study on the microstructure and thermal fatigue property of ZA38 Zn Al alloy with Si.

The experimental results show that the ZA38 alloy consists of primary α phase, (α +η) eutectoid and ε phase composition. After adding different content of Si element in ZA38 alloy, microstructure morphology have big difference, when Si addition amount is 0.55%, the degree of alloy organization’s refinement is the largest, from coarse dendritic structure without adding Si element is transformed into fine equiaxed grains and uniform distribution.

When the content of Si reached 0.55%, the tensile strength reached the maximum 405Mpa, compared with the alloy without Si element, it increased by 2.5%, and the elongation reached 4.33%, increased by 18.6%.. With the increase of Si content, the hardness of ZA38 alloy will increase.. However, when the content of Si in the alloy is too high, the bulk Si encounter in the alloy is obviously increased, which will separate the matrix, resulting in the stress concentration, and it will make the mechanical properties worse..

The thermal fatigue crack growth of ZA38 alloy is mainly influenced by two aspects: one is the strength and plasticity of the alloy, the other is the distribution of Si phase in the alloy. When the content of Si element in ZA38 alloy is 0.55%, the size of Si phase is moderate and uniform distribution in the matrix,. the microstructure of the alloy obtained maximum refinement, with the effect of thermal cycling should force, dislocation motion will be hindered, the thermal fatigue resistance of the alloy are improved. When the content of Si was too high, the primary Si phase was coarsening and distributed by the form of bulk and the strip on the matrix, the strength and ductility of the alloy were decreased, and the thermal fatigue resistance decreased greatly.. The thermal fatigue properties of ZA38 alloy are arranged from good to bad, followed by 0.55%Si, 0.3%Si, 0.8%Si, 0%Si, 1.3%Si, 1.05%Si.

Key Words  ZA38 alloy; microscopic structure; alloy mechanical properties; thermal fatigue property

 

 

第1章 緒 論

1.1 鋅基合金的簡介

1.1.1 鋅基合金的發(fā)展歷史

1930年，美國新澤西鋅合金公司研制出了Za2mak3和Zamak5鋅鋁壓鑄合金。二戰(zhàn)期間，德國為解決銅資源緊缺問題，成功的用重力鑄造鋅鋁合金代替銅合金制造軸瓦、軸套等軸承材料。1959-1962年，國際鉛鋅組織ILZRO發(fā)起了一項(xiàng)旨在開發(fā)新型的、先進(jìn)的壓鑄鋅鋁合金研制計劃，促使了薄壁鋅鋁合金壓鑄技術(shù)和ILZRO-16、ILZRO-12鑄造鋅合金的出現(xiàn)，ILZRO-12（后經(jīng)改進(jìn)發(fā)展成ZA12合金）的蠕變性能與Zamak3和Zamak5相當(dāng)，但其鑄造性能和力學(xué)性能更好[1]。上世紀(jì)70年代初期，加拿大Normand Mines Limited研究中心與美國 Zestern公司合作，研制出鋅基long-s metal減摩合金ZA8、ZA12、ZA27等。目前，美國、加拿大等發(fā)達(dá)國家有很多成功應(yīng)用鋅鋁合金的范例。