Effect of microstructure inhomogeneity on mechanical properties of different zones in TA15 electron beam welded joints

The effects of microstructure inhomogeneity on the mechanical properties of different zones in TA15 electron beam welded joints were investigated using a micromechanics-based finite element method.Considering the indentation size effect,the mechanical properties for constituent phases of the base metal(BM) and heat affected zone(HAZ) were determined by the instrumented nano-indentation test.The macroscopic mechanical properties of BM and HAZ obtained from the tensile test agree well with the numerical results.The incompatible deformation between the constituent phases tends to localize along the softer primary phase a where failure usually initiates in form of localized plastic strain.Compared with the BM,the mechanical properties of constituent phases in the HAZ differ substantially,leading to more serious strain localization behavior.

Microstructural Evolution and Softening Behavior of Simulated Heat-Affected Zone in 2219 Aluminum Alloy

The effect of peak temperature （Tp） at 200, 300, 400, 500 and 550 ℃ on the microstructural evolution and softening behavior of the simulated heat-affected zone （HAZ） was studied in the 2219-T87 alloy by electron-backscatter diffraction, transmission electron microscopy, X-ray diffraction, micro-hardness and micro-tensile tests. The results showed that the grain size in the HAZs at 200-500 ℃ was comparable, but the number density of the strengthening precipitates （GP zones/θ′） decreased with increasing Tp. At a Tp of 550 ℃, the grain size significantly decreased and the distribution of the misorientation angles corresponded to the MacKenzie distribution. The GP zones/θ′ phase coarsened and translated into θ phases at Tp values in the range of 200-400 ℃. Increasing the Tp to 500 ℃ and above, some θ′ phases translated into θ phases and others dissolved into the α-Al matrix which led to an increase in the solid solution strengthening. The reduction of the number density of the GP zones/θ′ was responsible for the softening behavior.

Underwater Wet Welding for HSLA Steels: Chemical Composition, Defects, Microstructures, and Mechanical Properties

The effect of water depth on underwater wet welds was investigated by underwater wet shielded metal-arc welding technique. The microstructures, chemical composition, welding defects, and mechanical properties were studied. The contents of alloying elements decrease, while the oxygen content increases with water depth. Within 55 m depth, the carbon monoxide reaction is controlling the oxygen content which will further control the contents of alloying elements. The columnar microstructures in weld metal obtained at shallow water consist of grain boundary ferrite, side-plate ferrite, and acicular ferrite, while those at depth greater than 11 m exhibit more proeutectoid ferrite due to the loss of alloying elements. Mechanical properties are a strong function of depth owing to the increase in oxidation of alloying elements and porosity. Welds obtained within 11 m show preferable strength, ductility, and toughness. The mechanical properties significantly drop from 11 to 25 m because of the increased porosity and oxidation of alloying elements.