工艺参数对Zn-4.5Cu-0.2Mn-0.3Bi合金水平连铸坯反偏析及凝固组织的影响

Effect of Technical Parameters on the Inverse Segregation and Solidification Structure of Horizontal Continuous Casting Billet of Zn-4.5Cu-0.2Mn-0.3Bi Alloy

研究了锌铜合金在电磁场下水平连铸坯的初生坯壳前沿位置变化规律,考察了铸坯横截面宏观组织、微观组织形貌及合金元素的分布。试验结果表明,坯壳前沿的位置是随着拉坯速度、浇注温度和电流强度的变化而变化的,其中尤以拉坯速度对其的影响最为明显。只有根据电流强度和浇注温度相对应调整拉坯速度才能达到改善组织和偏析的效果。较大的电流和拉坯速度促使坯壳前沿后移。当液-固界面位于冷却水套和搅拌器的交界处时,反偏析得到有效抑制。电磁场消除了普通水平连铸坯横截面组织不均匀、最后凝固点上移的现象。搅拌后上边缘和心部深灰色树枝状的富铜相并没有完全消失,只是尺寸略微变大,但边部和心部组织差异很小。当拉坯速度3 m/h、电流100 A时,边部和心部组织最为均匀细小,其他电流和频率时组织变化不大。Ti没有起到细化作用和抑制反偏析作用,反而使得液体变得粘稠,流动性变差。

The paper studied the change rule of the forepart of initial solidified shell, cross-section structure and elements distribution of horizontal continuous casting Zn-Cu alloy billets under electromagnetic field. The results show that the forepart position changes with the casting speed, pouring temperature and current intensity. Among these parameters, casting speed plays the most important role. It is only adjusting the corresponding casting speed according to the current strength and the pouring temperature that can improve the structure and reduce segregation. The forepart moves backwards by enhancing the current and the casting speeds. When the liquid-solid interface locates in the interspace between the cooling water jacket and the electromagnetic stirrer, the inverse segregation of Cu can be effectively suppressed. Electromagnetic field removes the nonuniform cross-section structures and the difference between the final solidification area and billet geometric center, and refines the dendrite structure. Stirring does not completely eliminate the deep gray dendritic copper rich phases in the edge or center of the billets, instead of slightly larger dendrite sizes and the small edge-center structure difference. When casting speed and current intensity is 3 m/h and 100 A, respectively, the most uniform and refined structure is obtained, while no obvious change can be seen for other currents and frequencies. The addition of Ti cannot refine the billet structure or eliminate the inverse segregation, but make the melt sticky with poor fluidity.