钛对7050铸轧板材裂纹调控的影响

Effect of trace titanium on the crack control of cast-rolling plate of 7050 aluminum alloy

摘要:

本文采用场发射高分辨扫描电子显微镜，差示扫描量热仪，X射线衍射仪等先进设备研究了微量Ti元素对7050铝合金铸轧薄板裂纹形成的影响规律和调控机理，结果表明：微量的Ti可以显著细化铸轧板的晶粒组织，改变晶粒生长方式，改善合金的流动性，使铸轧组织更加致密，消除合金内局部应力集中，抑制铸轧裂纹出现。而且，适量Ti元素还可以缩短铸轧7050铝合金的固液相线区间，减小晶核凝固前沿温度梯度，有效抑制成分偏析，从而降低晶界低熔点化合物数量，减少粗大第二相的产生，从而大幅增强铸轧铝合金的抗热裂能力。当7050铸轧板中Ti含量达到0.2%时，Ti对铸轧板裂纹的抑制作用最佳，而过量的Ti元素会聚集形成大块的含Ti脆性相，反而破坏组织的致密性，促进裂纹的萌生。

Abstract:

The influence and mechanism of Ti addition on the crack formation of twin-roll casting plates of 7050 aluminum alloys (TRC-7050) plates were studied with field-emission scanning electron microscopy (FESEM), differential scanning calorimetry (DSC), X-ray diffraction (XRD). The results showed that Ti addition significantly refine the grain sizes of the twin-roll casting plate, change the grain growth modes, improve the fluidity of the alloy, make the cast-rolled structure more dense, eliminate the local stress concentration in the alloy, and inhibit the occurrence of casting cracks. Appropriate amount of Ti addition can reduce the solid-liquid phase interval of the TRC-7050, reduce the temperature gradient of the nucleation solidification front and effectively inhibit the segregation of components, thereby reducing the number of low-melting compounds at the grain boundary and reducing the generation of coarse second phases, and then enhancing the resistance to the thermal cracking of the TRC-7050. 0.2 wt% Ti has the best inhibitory effect on the formation of TRC-7050 cracks. However, excess account of Ti addition will aggregate and form a sheet-like Ti-containing brittle phase, which subsequently will destroy the compactness of the structure and promote the initiation of cracks.