DC鑄造Al-12Si-0.65Mg-xMn合金中第二相的形成

DC鑄造Al-12Si-0.65Mg-xMn合金中第二相的形成FORMATION OF SECOND-PHASES IN A DIRECT-CHILL CASTING AL-12SI-0.65MG-xMN ALUMINUM ALLOY

采用LSCM、XRD、SEM、TEM及其附帶的EDS，結(jié)合相圖分析研究了DC鑄造Al-12Si-0.65Mg-(0~2.27)Mn(質(zhì)量分?jǐn)?shù), %)合金鑄錠中的第二相及其形成過(guò)程。結(jié)果表明，Al-12Si-0.65Mg合金鑄錠中存在α-Al、共晶Si、Mg2Si和π相(Al8Mg3FeSi6)，它們是分別在567℃通過(guò)L+Al5FeSi→α-Al+Si+Al8Mg3FeSi6、555℃通過(guò)L→α-Al+Si+Mg2Si及550-554℃通過(guò)L→α-Al+Si+Mg2Si+Al8Mg3FeSi6反應(yīng)形成的；當(dāng)合金中添加了Mn，α-Al枝晶明顯細(xì)化，同時(shí)合金鑄錠中出現(xiàn)α-Al(FeMn)Si相；當(dāng)Mn的質(zhì)量分?jǐn)?shù)從0.10%增大至2.27%，α-Al枝晶形貌、尺寸及數(shù)量無(wú)明顯變化，α-Al(FeMn)Si數(shù)量增多而尺寸不變；當(dāng)Mn的質(zhì)量分?jǐn)?shù)達(dá)到1.07%，合金在647℃通過(guò)L+Al6Mn→α-Al+Al9Mn4Si3反應(yīng)生成尺寸約80μm的Al9Mn4Si3，其中溶解了少量Fe形成為Al9(FeMn)4Si3，Mn含量增加其數(shù)量增多而尺寸不變；經(jīng)550℃均勻化處理后，合金中的Mg2Si相溶入基體消失，共晶Si、π相和α-Al(FeMn)Si相球化成顆粒狀，Al9(FeMn)4Si3相形貌、尺寸及數(shù)量幾乎不變，Al-12Si-0.65Mg-(0.10~2.27)Mn合金基體中析出尺寸約幾百納米的Al9(MnFe)2Si3彌散相粒子，其數(shù)量隨Mn含量增加而增多。

Mg-containing high Si aluminum alloy that can be heat treatment enhanced is widely used in the fields of engine, vehicle industry and aerospace, because of its high specific strength, high wear resistance, corrosion resistance and low thermal expansion coefficient. At present, the alloying to improve the microstructure of Mg-containing high Si aluminum alloy and improve its mechanical properties is an important research hotspot of this kind of alloy. As an important alloying element in aluminum alloy, Manganese is of great significance to study the type and formation process of Mn-containing second phase in Mg-containing high Si aluminum alloy. The second phases and their formation in a direct-chill casting Al-12Si-0.65Mg-(0~2.27)Mn (mass fraction, %) alloy were investigated by LSCM, XRD, SEM/EDS and TEM/EDS, combined with phase graph analysis. The results show that there are eutectic silicon, Mg2Si and π-(Al8Mg3FeSi6) besides matrix α-Al in the Mn-free Al-12Si-0.65Mg (mass fraction, %) alloy ingot, which are formed by the reactions of L+Al5FeSi→α-Al+Si+Al8Mg3FeSi6, L→α-Al+Si+Mg2Si and L→α-Al+Si+Mg2Si+Al8Mg3FeSi6 at 567℃, 555℃ and 550-554℃, respectively. The α-Al dendrites are obviously refined, and α-Al(FeMn)Si phase can be observed with the addition of Mn to Al-12Si-0.65Mg-(0.10~2.27)Mn (mass fraction, %) alloy ingot. With the Mn content increasing from 0.10% to 2.27%, the morphology of α-Al dendrites has no obvious change, and the number of α-Al(FeMn)Si increases gradually whereas the size of α-Al(FeMn)Si doesn’t change much. There are some Al9(FeMn)4Si3 with the size of about 80μm in the Al-12Si-0.65Mg-(1.07~2.27)Mn (mass fraction, %) alloy ingot with the Mn content over 1.07%, which are formed by the reaction of L+Al6Mn→(Al)+Al9Mn4Si3 at 647℃, and Al9Mn4Si3 turns into Al9(FeMn)4Si3 with Fe dissolved into it. The number of Al9(FeMn)4Si3 increases with the Mn content increasing from 1.07% to 2.27%, whereas the size of Al9(FeMn)4Si3 has no obvious change. Mg2Si entirely dissolves into the matrix. Eutectic silicon, π-(Al8Mg3FeSi6) and α-Al(FeMn)Si spheroidize into granules, whereas the size, the morphology and the numbe of Al9(FeMn)4Si3 remain unchanged after the Al-12Si-0.65Mg-xMn (mass fraction, %) alloy ingots were homogenized at 550℃. Simultaneously, there are many Al9(MnFe)2Si3 at hundreds of nanometer size precipitated out from the Al-12Si-0.65Mg-(0.10~2.27)Mn (mass fraction, %) alloy matrix after homogenization treatment, the number of them increases with the increasing of Mn content.

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