本文選題：A356合金 + Er�。� 參考：《江蘇理工學(xué)院》2017年碩士論文

【摘要】：A356鋁合金具有良好的綜合性能,合金的流動性好、氣密性小、收縮率小以及熱裂傾向性小。A356鋁合金具有亞共晶成分和較寬的固液共存區(qū),廣泛應(yīng)用在航空、汽車等領(lǐng)域。在鑄造條件下,A356鋁合金中初生α-Al枝晶較粗大,共晶Si容易形成粗大的針片狀,粗大的共晶Si使基體被嚴(yán)重割裂,合金的強(qiáng)度、塑性大大降低。因此為了提高合金的力學(xué)性能,通常采用變質(zhì)處理的方法。本文選用稀土Er作為細(xì)化劑,通過示差掃描量熱分析(DSC)、X射線衍射(XRD)、掃描電鏡(SEM)等分析手段來研究稀土Er對鑄態(tài)A356鋁合金組織和性能的影響。在分析出最佳稀土添加量的基礎(chǔ)上,對變質(zhì)后的合金進(jìn)行不同的熱處理,研究傳統(tǒng)T6工藝對合金的影響,并優(yōu)化工藝參數(shù),進(jìn)一步研究雙級時效對合金的影響。在經(jīng)稀土Er變質(zhì)的基礎(chǔ)上,添加微量元素Zr,研究復(fù)合變質(zhì)對鑄態(tài)合金組織和性能的影響。研究結(jié)果顯示:稀土Er可細(xì)化A356合金的初生α-Al相,而且可使共晶硅發(fā)生變質(zhì)。DSC分析可知稀土與鋁發(fā)生共晶反應(yīng),生成了α-Al和Al3Er化合物。而稀土共晶反應(yīng)先析出的α-Al可作為合金初生相的形核核心,細(xì)化晶粒,縮小二次枝晶間距。在硅相前沿,稀土Er元素容易形成成分過冷,使得硅相的原生長方向發(fā)生改變;部分吸附在硅相孿晶溝槽中的稀土原子嵌入了硅相晶格中,成為異類原子缺陷,引起晶格畸變,使硅在更多的方向產(chǎn)生孿晶,共晶硅的形貌發(fā)生改變,由粗大的板條狀轉(zhuǎn)變?yōu)榧?xì)小的粒狀、短棒狀,具有明顯的變質(zhì)作用。當(dāng)稀土Er元素含量為0.4%時,鑄態(tài)合金組織得到明顯改善,力學(xué)性能得到提高。A356+0.4%Er合金在T6工藝參數(shù)530℃×4h+175℃×6h下綜合性能較優(yōu)。同時研究了T6I6雙級時效工藝對A356+0.4%Er合金組織和性能的影響,優(yōu)化了工藝參數(shù)。當(dāng)預(yù)時效為110℃×2h,再時效為200℃×4h時,合金的抗拉強(qiáng)度、延伸率和硬度比T6工藝處理分別提高了11.9%、4.4%、18.2%。在A356+0.4%Er合金中添加微量的Zr,α-Al細(xì)化更顯著,硅相變質(zhì)效果更好。尤其當(dāng)Zr含量為0.2%,細(xì)化效果最佳,合金的抗拉強(qiáng)度可達(dá)225MPa,伸長率為6.4%,硬度為75.3HV,與單一Er元素變質(zhì)相比,分別提高了32.7%、4.9%、23.8%。
[Abstract]:A356 aluminum alloy has good comprehensive properties, good fluidity, low gas tightness, low shrinkage and small hot cracking tendency. A356 aluminum alloy has hypoeutectic composition and wide solid-liquid coexistence zone, which is widely used in aviation, automobile and other fields. The primary 偽 -Al dendrites in A356 aluminum alloy are coarse under casting conditions. The eutectic Si is easy to form coarse needle flake, the coarse eutectic Si makes the matrix be severed seriously, and the strength and plasticity of the alloy are greatly reduced. Therefore, in order to improve the mechanical properties of the alloy, the modification method is usually adopted. In this paper, rare earth er was used as the refiner, and the effect of rare earth er on the microstructure and properties of as-cast A356 aluminum alloy was studied by means of differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and so on. On the basis of analyzing the optimum amount of rare earth, different heat treatment was carried out on the modified alloy, the influence of traditional T6 process on the alloy was studied, and the technological parameters were optimized, and the effect of two-stage aging on the alloy was further studied. On the basis of rare earth er modification, the effect of complex modification on the microstructure and properties of as-cast alloys was studied by adding the trace element Zr. The results show that rare earth er can refine the primary 偽 -Al phase of A356 alloy, and the eutectic silicon can be modified by DSC. The results show that the rare earth reacts with aluminum to form 偽 -Al and Al3Er compounds. The 偽 -Al precipitated by the rare earth eutectic reaction can be used as the nucleation core of the primary phase of the alloy, refine the grain size and reduce the secondary dendrite spacing. At the front of silicon phase, rare earth er elements are easy to form subcooling elements, which make the original growth direction of silicon phase change, and some rare earth atoms adsorbed in silicon twin grooves are embedded in silicon phase lattice, resulting in defects of heterogeneous atoms, resulting in lattice distortion. The morphology of eutectic silicon is changed from coarse plate strip to fine grain shape, short bar shape and obvious metamorphism. When the content of rare earth er is 0.4, the microstructure of as-cast alloy is obviously improved, and the mechanical properties of .A356 0.4%Er alloy are improved at 530 鈩，

本文編號：1916855