材料期刊网

采用常温冲击实验和拉伸实验研究了大断面7050铝合金型材横向3个典型位置的力学性能的差异, 并通过OM, EBSD和TEM分析了其显微组织. 结果表明: 晶粒尺寸约为12 μm的型材芯部比晶粒尺寸约为6 μm的边部的屈服强度高, 其原因是芯部较硬Copper取向的形变织构组分更强. 根据固溶合金元素含量所得的固溶强化项、亚晶粒尺寸所得的晶界强化项和合金的屈服强度可计算Taylor因子, 芯部为3.925, 边部为2.257. 晶界强化模型中Hall-Petch模型比Nes模型更适用于计算固溶后的晶界强化对合金屈服强度的贡献. 此外, 还建立了3种试样过时效态冲击功与亚晶粒尺寸之间的线性关系.

Generally, it is believed that inside the material the smaller grain size is, the higher yield strength is. In addition to this effect, grain refinement method also ensures that the toughness of the material is not reduced. However, it is found that the relationship between the grain size distribution and mechanical properties is contradiction with this law after the properties have been studied in the transverse direction of a large cross-section 7050 aluminum alloy profile. That is, the impact energy and yield strength in the center with a large grain size is higher than those at the edge with the smaller grain size in the thickest section of the profile. Besides that, during the establishment of the yield strength model in over-aging 7050 aluminum alloy, there are two models for the grain boundary strengthening which are Nes model and Hall-Petch model, so the choice from these model is found to affect the final results of the yield strength model. In order to study and understand the reasons for this phenomenon, the difference of mechanical properties distribution in the cross-section of 7050 aluminum extrusion profile has been investigated by impact test and tensile test at normal temperature, meanwhile, the microstructures have been analyzed by OM, EBSD and TEM. The results show that lots of the harder deformation textures, i.e., copper texture in the core of the profile lead to higher yield strength in the core with grain size of 12 mm than that in the edge with grain size of 6 mm. The Taylor factor could be calculated after the solution strengthening by alloying elements, grain boundary strengthening by the sub-grain and the yield stress of the alloy, at last, it reaches to 3.925 in the core, while that is just 2.257 in the edge. Compared with Nes model, the Hall-Petch model is much preferable to the calculation of grain boundary strengthening in yield stress of 7050 aluminum alloys after solid solution treatment. It is established that there is a linear relationship between impact energy and grain size of three over-aging specimens.