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.

Study on dryout point and heat transfer in subcooled flow boiling through vertical narrow annular channels

The purpose of this study is to conduct the dryout point and heat transfer correlation for subcooled boiling flow in narrow annuli. First, the dryout point of subcooled flow boiling of water was measured in narrow annular channels under the working condition of pressure ranging from 0.1 to 0.3 MPa and low mass flow rate from 6 to 60 kgm^-2 s^-1. Experimental test channels were annular and heated bilaterally with the channel gap of lmm and 1.5mm, and heated length of 1500mm.The location of the dryout was observed and measured by experiment with investigating the various system parameter effects on dryout point, and the results show that the location of dryout point is basically stable and repeating and the heat transfer coefficient increased with heat flux, mass flux and pressure, however, decreases with the gap size. Next, new correlations of CHF and critical vapor quality for narrow annular channels was proposed and calculation results shown a good agreement with the experimental data.

Dynamics of buoyancy-driven microflow in a narrow annular space

This paper aims to investigate the dynamics of buoyancy-driven microflow in a narrow annular space inside a liquid floated gyroscope(LFG). Several theoretical models with a non-uniform thermal boundary for fluid flow in annular channels are given to analyze the effects of various parameters, such as the clearance size h, roughness height re, and rough density ε, on the flow and temperature profiles as well as on the fluid-drag torque. In the narrow annular regime, the relationship between the temperature and the angular displacement of the outer wall is defined as a cosine function, and the surface roughness of the inner wall is structured as a series of surface protrusions with a circular shape. With the increase of clearance size h, the flow velocity gradually increases to a stable level, and the drag torque increases initially and then decreases to a stable level. Furthermore, the increase of roughness height re and roughness density ε intensifies the frictional effect of fluid on the inner-wall surface. However, these two parameters have no significant effect on the flow velocity. This study can provide theoretical references for precision manufacturing and precision improvement of gyro instruments.

Infl uence of Heat Treatment on Precipitation Behavior and Mechanical Properties of Extruded AZ80 Magnesium Alloy

By means of annular channel angular extrusion technology and solution treatment,the AZ80 supersaturated solid solu-tion was prepared.Theβ-Mg 17 Al 12 precipitate morphologies analysis along with its sizes and area fraction measurement was performed to investigate mechanical properties variation of alloy at various aging temperature.The results indicated that after solution treatment,the intergranular precipitate of as-extruded alloy was re-dissolved into the matrix,eff ectively decreasing the stress concentration,which was benefi cial to the enhancement of elongation.At aging temperatures of 300°C,Widmanstatten structure,lath-shaped precipitate,and intergranular precipitate were observed,while at 175–200°C,cellular structure and oval-shaped particle were also identifi ed.The morphology,area fraction,size of the precipitates,and PFZs(precipitate free zones)width worked together to aff ect the age-hardening behavior of the alloy.The strength and hardness of the peak-aged samples decreased with the increase in aging temperature,which is primarily attributed to the reduction in cellular structure area fraction and the corresponding increase in the interlamellar spacing,and the coarsening of the rhombus precipitate.

Experimental Investigation of Bubble Behaviors in Subcooled Flow Boiling

The experimental investigation on vapor bubble growth is performed for analyzing subcooled boiling in a vertical annular channel with inner heating surface and upward water flow under atmospheric pressure. Bulk liquid mass flux ranges from 79 kg/m2s to 316 kg/m2s, and subcooling is from 40 K to 60 K. The bubble behaviors from inception to collapse are captured by High-speed photography. The performance of bubble growth recorded by the high-speed photography is given in this paper. The bubble behaviors, effect of the bubble slippage on the heat transfer, and various forces acting on the bubble are discussed.