Comparisons of microstructure homogeneity,texture and mechanical properties of AZ80 magnesium alloy fabricated by annular channel angular extrusion and backward extrusion

This paper provided an efficient single pass severe plastic deformation(SPD)method,annular channel angular extrusion(ACAE),for fabricating AZ80 magnesium alloy shell part.The effect of ACAE process on the microstructure homogeneity,texture,and mechanical properties of extruded part was experimentally investigated.For comparison,conventional backward extrusion(BE)was also conducted on processing AZ80 part with same specification.The results showed that ACAE process has a better capacity to refine the microstructure and dramatic improve the deformation homogeneity of the extruded part than BE process.Due to two strong shear deformations were implemented,ACAE process could also concurrently modify the basal texture more notably than BE process.In particular,a bimodal texture was found in ACAE extruded part,which was greatly related to the enhanced synergetic action of basal slip and secondary<c+a>slip caused by the effective shear stress.More uniform and superior hardness along the thickness and height of part were achieved via ACAE process.Further surveying of tensile tests also showed that the part fabricated by ACAE process exhibited significantly higher and far more homogeneous tensile properties with an excellent balance of strength and ductility.The remarkable enhanced tensile properties of ACAE extruded part could be primarily attributed to the significant grain refinement,which provided a powerful grain boundary strengthening effect and meaningfully suppressed the development of twin-sized cracks during tensile deformation.It was established that ACAE process seemed to be a very promising single pass SPD method for manufacturing Mg-based alloy shell parts with more homogeneous microstructure and superior performance.

High Strength and Excellent Ductility of AZ80 Magnesium Alloy Cabin Component Developed by W-Shaped Channel Extrusion and Subsequent T6 Heat Treatment

The AZ80 magnesium(Mg)alloy cabin component with high strength and excellent ductility was developed by W-shaped channel extrusion(WCE)at 350℃ and subsequent T6 heat treatment.The effect of WCE process on the microstructure and mechanical properties of the alloy was experimentally investigated,and the age-hardening behavior with microstructure evolution during heat treatment was revealed.Due to the introduction of multi-stage asymmetric extrusion and severe shear deformation along the annular channel,the average grain size of the WCE extruded alloy could be effectively refined to 4.7μm.Besides,theβphase particles were dynamically precipitated from the fine grain boundaries during extrusion,which hindered the grain growth,but worsen the material plasticity.After T6 treatment,the properties of component were eventually improved to a yield strength(YS)of 218 MPa and ultimate tensile strength(UTS)of 344 MPa with elongation(EL)of 14.5%.It was revealed that the rod/lath-and needle-shaped continuousβphase(CP)with finer size precipitated after T6 treatment was more effective in hindering the movement of dislocations and strengthened the alloy than lamellar discontinuousβphase(DP).The dispersed phase precipitated in the grains,the annihilation of dislocations,the uniformly distributed grains and the re-dissolution ofβphase particles at initial grain boundaries after T6 treatment greatly contributed to the ductility of alloy.Moreover,the T6 treatment also promoted the basal plane of most grains which were re-arranged to the extrusion direction,which promoted the possibility of non-basal slip activation and further improved the elongation of the alloy.As a result,the UTS and YS of the final component increased by 10%and the EL increased by 7%,respectively.

Nitrogen fluorescence induced by the femtosecond intense laser pulses in air

Our experiments show that external focusing and initial laser energy strongly influences filament generated by the femtosecond Ti–sapphire laser in air. The experimental measurements show the filament length can be extended both by increasing the laser energy and focal length of focusing lens. On the other hand, the plasma fluorescence emission can be enhanced by increasing the laser energy with fixed focal length or decreasing the focal length. In addition, the collapse distance measured experimentally are larger than the calculated ones owing to the group-velocity-dispersion effect. In addition, we find that the line widths of the spectral lines from N2 is independent of filament positions, laser energies and external focusing.

Ultrafast dynamical process of Ge irradiated by the femtosecond laser pulses

The ultrafast dynamic process in semiconductor Ge irradiated by the femtosecond laser pulses is numerically simulated on the basis of van Driel system. It is found that with the increase of depth, the carrier density and lattice temperature decrease, while the carrier temperature first increases and then drops. The laser fluence has a great influence on the ultrafast dynamical process in Ge. As the laser fluence remains a constant value, though the overall evolution of the carrier density and lattice temperature is almost independent of pulse duration and laser intensity, increasing the laser intensity will be more effective than increasing the pulse duration in the generation of carriers. Irradiating the Ge sample by the femtosecond double pulses, the ultrafast dynamical process of semiconductor can be affected by the temporal interval between the double pulses.