釔含量對(duì)MgZn4.5YxZr0.5合金熱裂敏感性的影響

釔含量對(duì)MgZn4.5YxZr0.5合金熱裂敏感性的影響Effect of yttrium content on hot tearing susceptibility of MgZn4.5YxZr0.5 alloys

采用熱分析法和鑄造熱裂試驗(yàn)研究MgZn4.5YxZr0.5(x=0.5，1，2，4，6(質(zhì)量分?jǐn)?shù), %))合金的熱裂行為。結(jié)果表明：MgZn4.5Y1Zr0.5合金的枝晶干涉溫度Tcoh最高、在脆弱區(qū)域的溫度差ΔTc最大、在最后凝固階段剩余的液相量最少、形成的液膜厚度較薄，補(bǔ)縮程度較低，所能抵御的凝固收縮力最小、裂紋擴(kuò)展速率最大。這些現(xiàn)象說明MgZn4.5Y1Zr0.5合金具有最高的熱裂敏感性。隨著Y含量的增加，聚集在晶界處的低熔點(diǎn)相對(duì)合金熱裂行為的作用以及合金的熱裂形成機(jī)制均發(fā)生變化：當(dāng)Y含量不超過1%時(shí)，低熔點(diǎn)相主要對(duì)晶間結(jié)合力起破壞作用，合金的熱裂形成機(jī)制主要是晶間搭橋的斷裂；當(dāng)Y含量超過1%時(shí)，低熔點(diǎn)相主要對(duì)枝晶分離區(qū)起補(bǔ)縮作用，合金的熱裂形成機(jī)制為晶間搭橋、枝晶分離區(qū)域的補(bǔ)縮和液膜共同作用。

Thermal analysis method and constrained rod casting (CRC) were used to study hot tearing behavior of MgZn4.5YxZr0.5 (x=0.5, 1, 2, 4, 6 (mass fraction, %)) alloys. The results show that MgZn4.5Y1Zr0.5 alloy possesses the highest hot tearing susceptibility (HTS) among the tested alloys due to the highest coherency temperature (Tcoh), the largest temperature difference (ΔTc) in vulnerable region, the least residual liquid in last stage of solidification, the lowest anti-contraction force of thinner film, the poorer feeding capability and the highest crack propagation rate. The role of low-melting point phases gathering at grain boundary on the HTS and the main mechanism of hot tearing shift gradually with different Y contents: when Y is not more than 1%, the role is mainly a damaging effect on intergranular binding force and the main mechanism is fracture of intergranular bridges; when Y is more than 1%, the role is mainly an intergranular feeding effect on formed separated dendrites and the main mechanism is the collective effect of intergranular bridges, intergranular feeding and film.

全文下載：https://pan.baidu.com/s/1skEo2sd