不同轧制压下率铝/钢复合板界面及断裂分析

Interface and Fracture Analysis of Al/steel Clad Plate under Different Reduction Rates

对液-固双辊铸轧法制备的铝/低碳钢复合板经450℃退火1.5 h后进行三道次轧制处理,每道次轧制处理后复合板压下率分别为25%、35%和45%。利用SEM和EDS观察界面组织并分析元素分布,通过原位拉伸试验观察复合板失效过程,测试其抗拉强度和伸长率。结果发现,退火态复合板界面处存在连续的扩散层,轧制态复合界面处扩散层在压力作用下破碎成块状,且压下率越大,扩散层厚度及其破碎的块状尺寸越小。25%和35%压下率复合板界面处存在明显裂纹及孔洞,45%压下率复合板界面处裂纹消失。退火态复合板A356铝合金侧主裂纹源于共晶Si颗粒和偏析共晶Si颗粒处,45%压下率复合板的主裂纹是由铝基体处的小裂纹迅速扩展而形成。45%压下率复合板具有最好的界面结合品质、良好的协调变形能力,抗拉强度达441 MPa,且伸长率为3.03%。

The aluminum/low carbon steel clad plate were fabricated by liquid-solid twin-roll casting, after annealing at 450 ℃ for 1.5 h and rolled for three passes. After each pass rolling treatment, the reduction rate of the clad plates reaches 25%, 35% and 45%, respectively. The microstructure was observed and the element distribution of the interface was analyzed by SEM and EDS. The failure process of the clad plates was observed by in-situ tension, and the tensile strength and elongation were tested. The results indicate that there exists a continuous diffusion layer at the interface of the annealed clad plates, and the diffusion layer is broken into blocks under the pressure of the twin roll. Moreover, the greater the reduction rate is, the thinner the diffusion layer is, and the smaller the blocks is. Obvious gaps and holes are observed at the interface with the reduction rate of 25% and 35%, which disappear when reduction rate reaches 45%. The main cracks on the A356 side of annealed clad plates are originated from eutectic silicon particles and segregated eutectic silicon particles, and that of clad plates with reduction rate of 45% are formed by the rapid propagation of small cracks in the aluminum matrix. The clad plates with reduction rate of 45% exhibit the optimal bonding strength of interface and desirable ability of coordinated deformation, where the tensile strength reaches 441 MPa, and the elongation is 3.03%.