The bending properties of 6000 series Al alloys are affected by the precipitates, shear band generation, preferred orientation, and residual stress distribution. Such alloys are characterized by initial cracks of extruded profiles that initiate at depths of 100–200 μm. Studies have used TEM to investigate the effect of precipitates. However, it is also important to evaluate the energetic stability of the grain boundaries and grain matrix around the crack origin at a micro level. To clarify the crack initiation mechanism, we considered the kernel average misorientation (KAM) and sigma (Σ) value at the crack initiation point. In cross sections from the surface region up to a depth of 400 μm, A6061 showed 15% more low-order Σ values of 3, 5, and 7, indicating that it had an energetically stable and strong interface compared to A6005C. The KAM map and Σ value of the surrounding area were obtained using electron backscatter diffraction measurements. The KAM map indicated that the initial crack occurred at the grain boundary with a high strain concentration and high Σ value. STEM-EDS results revealed precipitates in the grain matrix of AlMgSiCu-based Q or Q’ compounds. Their number density and PFZ width were almost the same, and they had only a small effect on crack initiation. However, the morphology of the precipitates in A6061 was smaller than that in A6005C; this may affect the strain distribution in the grain matrix. Thus, we focused on the energetic stability of the grain boundaries and grain matrix and found that cracks initiated at unstable grain boundaries with a large Σ value where strain was concentrated when a tensile force was applied.

6000 系列铝合金的弯曲性能受析出物、剪切带生成、择优取向和残余应力分布的影响。这种合金的特点是挤压型材的初始裂纹始于 100-200 微米的深度。研究已经使用 TEM 来研究沉淀物的影响。然而，在微观水平上评估裂纹起源周围晶界和晶粒基质的能量稳定性也很重要。为了阐明裂纹萌生机制，我们考虑了裂纹萌生点的核平均取向错误 (KAM) 和 sigma (Σ) 值。在从表面区域到 400 μm 深度的横截面中，A6061 的 3、5 和 7 低阶 Σ 值增加了 15%，表明与 A6005C 相比，它具有能量稳定且坚固的界面。使用电子背散射衍射测量获得周围区域的 KAM 图和 Σ 值。KAM图表明初始裂纹发生在晶界处，具有高应变浓度和高Σ值。STEM-EDS 结果显示 AlMgSiCu 基 Q 或 Q' 化合物的晶粒基质中有沉淀物。它们的数量密度和 PFZ 宽度几乎相同，它们对裂纹萌生的影响很小。但A6061的析出物形貌比A6005C小；这可能会影响晶粒基质中的应变分布。因此，我们专注于晶界和晶粒基质的能量稳定性，发现裂纹在不稳定的晶界处开始，具有较大的 Σ 值，在施加张力时应变集中。