钛对7050铸轧板材显微组织和裂纹调控的影响

Effect of Ti Addition on Microstructures and Crack Behavior of Twin-Roll Cast-Rolled 7050 Alloy Plate

采用场发射扫描电子显微镜,差示扫描量热仪,X射线衍射仪等设备研究了微量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%(质量分数),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。

The influence and mechanism of Ti addition on the crack formation of twin-roll cast-rolled plates of 7050 aluminum alloys(TRC-7050)were studied with field-emission scanning electron microscopy(FESEM),differential scanning calorimetry(DSC),and X-ray diffraction(XRD).The results show that Ti addition can 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 denser,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 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 Ti addition will aggregate and form a sheet-like Ti-containing brittle phase,which will subsequently destroy the compactness of the structure and promote the initiation of cracks.