The fatigue characteristic of 2124 aluminum alloy in T851 condition was investigated by means of scanning electron microscopy (SEM) and transmission electron microscope (TEM). And the result shows that, the fatigue life is closely related to the thickness of plates, this is because that different thickness of plates results in the variation of grain size, grain boundaries and substructures of alloy, which thus influence the fatigue behavior of 2124-T851 alloy. The number of grain boundaries along the propagation direction of cracks and the amount of substructures after heat treatment increase with the decline of thicknesses of 2124 alloy plates, while the grain size is reverse. However, no obvious size and dispersion changes for the precipitates. Comparatively, the fatigue resistance performance of 30mm thickness plate is better than the 40mm and 55mm thickness plates, which is due to the more profitable grain size, grain boundary and substructure.

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Al-Mg alloy plates with 10mm thick were welded by multi-pass MIG welding with the self-made wire as filler material, and microstructure of the welded joint were examined by metallographic and electron backscatter diffraction (EBSD). The results indicate, because of the grain refining effect of Zr, the grains in welding joints fusion zone formed grain-refining layer tissue by competitive growth. In the juncture zone of two welding passes, because of the grain epitaxial growth mechanism, it formed obvious coarse grain zone, which became a weak link of welding joints. And the coarse grain zone exist faint <110> texture, but to the whole, the welding zone did not exist obvious preferred orientation.

Observation of fratcure morphology and energy spectrum analysis of fracture toughness specimens of high strength aluminum alloy was carried out on scanning electron microscope (SEM), and the fracture behaviour of this alloy has also been studied. It is revealed that the fracture surface can be divided into 3 regions: precrack region, propagation region and rapid fracture region, the appearance of which is similar to that of cleavage fracture, mixed mode fracture and static fracture, respectively. The fracture of high strength aluminum alloy is primarily influenced by coarsed Fe-rich particles which is relatively brittle, and the major fracture mode of this kind of alloy is toughness fracture casued by coarsed second phase particles.