Metal flow hysteresis behavior and shape control strategy during porthole die extrusion of micro heat pipe

The shape control strategy of micro grooves is still unclear and challenging during the porthole die extrusion of grooved micro heat pipe(MHP).Through the simulation and experiment of porthole die extrusion of a MHP profile,the metal flow hysteresis behavior within micro features and the effect of ram speed and extrusion temperature on it and the resulting forming integrity was elucidated.Innovatively,Taguchi design and variance analysis(ANOVA)were introduced to determine their influence magnitude on the metal flow uniformity calculated by simulation results.The main findings are given below.The metal flow hysteresis derives from part feature size effect.The negligible friction-affected area during conventional extrusion severely slows down the metal flow within micro features during the MHP profile extrusion,which is due to the surge in the area ratio of the friction-affected area to the region in which it is located.Neither ram speed nor extrusion temperature can change the distribution of the friction-affected area.However,increasing ram speed multiplies the metal flow hysteresis and severely reduces the forming integrity,whereas extrusion temperature has little effect.Following this strategy,batch extrusion of the profile with microgrooved width of 0.27±0.02 mm was achieved in industrialized conditions.

Achieving three-layered Al/Mg/Al sheet via combining porthole die co-extrusion and hot forging

Al/Mg/Al sheet with good bonding quality and mechanical properties was fabricated based on the proposed porthole die co-extrusion and forging(PCE-F)process.There were no voids,cracks or other defects on the Al/Mg interface.A continuous diffusion zone with two-sub-layer structure was formed across the Al/Mg interface,and its width increased with higher temperature or reduction ratio.The sub-layers formed at low and high temperature were identified to be solid solutions and intermetallic compounds(IMCs)including y-MgpAl^and^-Al3Mg.In Al layer,the welding zone mainly consisted of fine equiaxed grains with several coarse elongated grains,while the majority of matrix zone is coarse elongated grains.The rolling textures were dominated in both welding and matrix zones.In Mg layer,the welding zone exhibited complete DRXed grain structure,while several unDRXed coarse grains were observed in the matrix zone.With the increasing temperature,the grain size of Al and Mg layer firstly decreased and then increased.High reduction ratio strongly refined the grain structure of Al layer,while slightly affected the Mg layer.The Al/Mg/AI sheet experienced stress-drops twice during the tensile test.The first stress-drop was determined by the IMCs and microstructure of Mg layer,while the second stress-drop was closely related to the microstructure of Al layer.Al/Mg/Al sheet forged at the lowest temperature without the formation IMCs exhibited the highest stress for the first stress-drop,and that forged under the highest reduction ratio with the smallest grain size in Al layer had the highest stress for the second stress-drop.

Formation mechanism and evolution of surface coarse grains on a ZK60 Mg profile extruded by a porthole die

Porthole die extrusion of Mg alloys was studied by means of experimental and numerical studies. Results indicated that an inhomogeneous microstructure formed on the cross-section of the extruded profile. On the profile surface, abnormal coarse grains with an orientation of <11-20> in parallel to ED(extrusion direction) appeared. In the profile center, the welding zone was composed of fine grains with an average size of 4.19 um and an orientation of <10-10> in parallel to ED, while the matrix zone exhibited a bimodal grain structure. Disk-like, near-spherical and rod-like precipitates were observed, and the number density of those features was lower on the profile surface than that in the profile center. Then, the formation and evolution of coarse grains on the profile surface were investigated, which were found to depend on the competition between static recrystallization and grain growth. The stored deformation energy was the factor dominating the surface structure through effective regulation over nucleation of the precipitates and recrystallization. A profile with a low stored deformation energy suppressed formation of precipitates and consequently facilitated grain growth rather than recrystallization, resulting in the formation of abnormal coarse grains. Finally, the surface coarse grains contributed detrimentally to hardness, tensile properties, and wear performance of the bulk structure.

Formability evaluation of AZ31B extruded tube for hydroforming process

Hydroforming of magnesium and aluminum alloy tube at elevated temperature is becoming a very promising method to manufacture light-weight hollow components.Uniaxial tensile test and hydrobulging test were used to investigate the formability of AZ31B magnesium tube at different temperatures.The tube was manufactured by porthole die extrusion.Results show that as temperature increase,the tension formability along the extrusion direction measured by tensile test increases significantly,whereas the maximum hydrobulging ratio measured by hydrobulging test does not change accordingly.This anisotropy character of the tube,i.e.,different properties in axial direction and hoop direction,is mainly dependant on the extrusion process.In addition,there exists several weld lines along the extrusion direction.These weld lines will become the weakest positions when formed at elevated temperature,and will consequently decrease the formability of the tube during hydroforming process.