Search

A new plastic processing method for laser bending of TC4 titanium alloy heavy plates was developed in this work. Different from previous studies, the thickness of the plates in this work reached 6 and 12 mm. High-energy laser beam was applied on the surface of the TC4 titanium alloy heavy plate, resulting in thermal stress on the surface of the plate and causing bending deformation. The microstructure and mechanical properties of the bended plates were investigated. A finite element model was also developed to simulate the laser-assisted bending process of the TC4 titanium alloy heavy plate. The microstructure observation indicates that the original α + β worm-like microstructure changed to basket-weave microstructure composed of α′ phase of acicular martensite after laser bending. This microstructure with high densities of dislocation and twinning played an important role in grain boundary strengthening. Therefore, the hardness of the center of the heat-affected zone > the hardness of the base metal > the hardness of the edge of the heat-affected zone after bending. The tensile strength of the heat-affected zone is not significantly different from that of the base metal, but the tensile elongation is slightly lower than that of the base metal and its plasticity is lower. The simulation implies that temperature gradients in the normal direction caused by laser scanning can stimulate a horizontal partial stress σ x. The variation of σ x causes the plate form a bending angle after laser scanning. [ABSTRACT FROM AUTHOR]

In this work, Mg-3Y sheet was prepared by high temperature cross-rolling and subsequent short-term annealing. The effect of annealing on microstructure, texture, mechanical properties, and stretch formability of Mg-3Y sheet was primarily investigated. Micro-nano size coexistence of β-Mg24Y5 phases can be well deformed with matrix. The as-rolled Mg-3Y sheet exhibited a homogeneous deformation microstructure consisting of deformed grains with extensive kink bands and dispersed β-Mg24Y5 phases. A double peak texture character appeared in as-rolled Mg-3Y sheet with a split of the texture peaks of about ±20° tilted to rolling direction. After annealing, the as-annealed Mg-3Y sheet presented complete static recrystallized (SRXed) microstructure consisting of uniform equiaxed grains. The texture orientation distribution was more dispersed and a weakened multiple-peak texture orientation distribution appeared. In addition, the maximum intensity of basal plane decreased from 5.2 to 3.1. The change of texture character was attributed to static recrystallization (SRX) induced by kink bands and grain boundaries. The as-annealed Mg-3Y sheet with high Schmid factor (SF) for basal slip, prismatic slip, pyramidal slip, and pyramidal slip exhibited high ductility (~25.6%). Simultaneously, enhanced activity of basal slip and randomized grain orientation played a significant role in decreasing anisotropy for the as-annealed Mg-3Y sheet, which contributed to the formation of high stretch formability (~6.2 mm) at room temperature. [ABSTRACT FROM AUTHOR]

The effect of low-frequency electromagnetic field (LFEF) on temperature pattern and microstructure on both symmetry planes was investigated during the semi-continuous direct chilling (DC) casting process of magnesium slab. The distribution characteristics of magnetic flux density (B) and time average electromagnetic volume force density (F) were calculated. The weak value ofFwas found near the slab corner, which was clearly distinguished from the distribution ofB. According to the temperature measurement results, LFEF made the mushy region much flatter than that of conventional DC casting and it was much more obvious in the thickness direction. Compared with conventional DC casting, the low-frequency electromagnetic casting (LFEC) process could decrease the average temperature gradient between the centre and border in the mushy zone. The microstructures on both symmetry planes were also refined at different levels during the LFEC process. [ABSTRACT FROM PUBLISHER]

Highlights: [•] The hot deformation behavior of a newly Mg–9d–3Y–2Zn–0.5Zr alloy was studied. [•] The form of the flow stress curves was sensitive to temperature and strain rate. [•] The processing map at the strain of 0.5 representing steady-state flow was developed. [•] The microstructures evolution and dynamic recrystallized (DRX) were analyzed. [•] The optimum deformation condition was at 450°C with the strain rate of 0.01s−1. [ABSTRACT FROM AUTHOR]

Abstract: The influence of low frequency electromagnetic field and power ultrasonic field on the microstructure of AZ80Mg alloy billets was studied. The magnetic flux density and time average electromagnetic volume force density were obtained by numerical simulation. The acoustic pressure distribution was also numerically calculated in order to characterize the ultrasonic field propagation. After comparison of the different effects of grain refinement by low frequency electromagnetic casting (LFEC) and ultrasonic casting (UC), a new method (LFEC+UC) was developed by simultaneously applying ultrasonic vibration to the melt during low frequency electromagnetic semi-continuous casting of AZ80Mg alloy billets. With the application of the compound field under the optimum conditions, the as-cast macrostructure and microstructure were refined and homogeneously distributed. An obvious improvement of mechanical properties was finally obtained. The mechanisms of grain refinement and interaction of low frequency electromagnetic field and power ultrasonic field with the melt were discussed. [Copyright &y& Elsevier]