Combination of eddy current and heat treatment for crack healing and mechanical-property improvement in magnesium alloy tube

The continuous eddy current pulse treatment(ECPT)combined with heat treatment was employed to heal the microcracks in spin formed Mg alloy tubes and improve their mechanical properties in this study.The results show that all the microcracks in different tube specimens were almost healed after different continuous ECPT schemes up to 15 cycles.The schemes with less cooling intervals exhibited better healing effect and increased the strength and elongation of Mg alloy tubes more obviously.After aging treatment,the strength improvement of the specimens with ECPT was more remarkable than that of the specimens without ECPT,and the elongation decrease of the specimens with ECPT was less evident than that of specimens without ECPT due to the segregation of RE elements on the crack surface.Besides,after solution treatment,the strength reduction and ductility improvement of the specimens with ECPT were more pronounced than that of the specimens without ECPT owing to the notable decrease of dislocation density of the specimens with ECPT.Both narrowed cracks induced by ECPT and the segregation of precipitates in the vicinity of microcrack surface during aging treatment contributed to the maximum strength in the as-spun specimens with ECPT followed by aging treatment.

Effect of power spinning and heat treatment on microstructure evolution and mechanical properties of duplex low-cost titanium alloy

The microstructural evolution and mechanical properties of low-cost Ti-5.5Al-1Fe-3.5Cr-3.2Zr-0.2Si al-loy during power spinning and after three types of heat-treatment routines(low-temperature anneal-ing,high-temperature annealing,solution and annealing)were systematically studied.An effective heat-treatment routine to fabricate high-strength and acceptable ductile as-spun Ti-5.5Al-1Fe-3.5Cr-3.2Zr-0.2Si alloy tubes was then proposed whereby the relationship between the mechanical performances and mi-crostructures was analyzed.The{0002}_(α)and{001}_(β)textures were formed after multi-pass power spin-ning.The as-spun LC-Ti alloy exhibited a good combination of strength and elongation after heat treat-ment at 550℃for 4 h,which was ascribed to the large plastic induced low-temperature spheroidization of deformedαphase and nanoscaleαprecipitation from deformedβphase.However,the elongation de-creased evidently when Zr2Si/TiCr2 participated at the interphase boundaries after heat treatment at 550℃for 8 h.In high-temperature annealing,the elongation changed nonlinearly owing to the precipitation of Zr2Si particles at triangular grain boundaries treated at 750℃for 1 h,and the spheroidization of the deformedα_(p)phase.Under solution and annealing conditions,lenticularαs would participate from the metastableβgrains,which contributed to the greatest strength albeit poor ductility.This study provides an effective guidance for the processing and application of the low-cost titanium alloy.

Analysis of abnormal texture formation and strengthening mechanism in an extruded Mg-Gd-Y-Zn-Zr alloy

A Mg-Gd-Y-Zn-Zr magnesium alloy with different initial states was extruded under different extrusion parameters.The effect of solution treatment and extrusion parameters on the microstructure,texture and mechanical properties were analyzed in detail,and the abnormal texture formation and strengthening mechanism was revealed.When extruded at low temperature and small extrusion ratio,the bimodal microstructure consisting of fine dynamically recrystallized grains and coarse deformed grains occurred both in the as-cast alloy and solution-treated alloy.When the extrusion temperature and extrusion ratio were increased,the amount and size of dynamically recrystallized grains increased and the grain size of the solution-treated alloy showed higher growth rate.Furthermore,an abnormal texture with<0001>parallel with extrusion direction developed due to the occurrence of non-basal slip and continuous dynamic recrystallization.This could be enhanced by solution treatment,high temperature,and large extrusion ratio.Both the as-cast alloy and solution-treated alloy exhibited the highest tensile strength after extrusion at 300℃with an extrusion ratio of 9.Grain refinement was the main strengthening mechanism utilized in both the as-cast alloy and the solution-treated alloy.Work hardening played an important role in the sample extruded at low temperature and small extrusion ratio,with the highest contribution of about 33 MPa after extrusion at 300℃with an extrusion ratio of 9.Texture strengthening contributed more in the sample extruded at high temperature and large extrusion ratio,but no more than 24.1 MPa.Solution strengthening was another strengthening mechanism in the extruded as-cast alloy,especially at high temperature and large extrusion ratio(no more than 9 MPa).

Process design and microstructure-property evolution during shear spinning of Ti_(2)AlNb-based alloy

Rotationally symmetric workpieces of Ti_(2)AlNb-based alloys have great potential for high-temperature service condition in aviation industry,while the poor workability limits their application until now.In this study,shear spinning and heat treatment were first conducted to investigate the corresponding microstructure evolution and mechanical properties of Ti_(2)AlNb conical workpieces.The microstructure of the 1^(st) and 2^(nd) pass spun workpieces(SP1 and SP2)mainly consisted of B2+retainedα2phases.After two passes spinning,the B2 phase texture changed from<111>//ND of as-received alloy to be<001>//ND.The ultimate tensile stress(UTS)of SP1 and SP2 was increased to 1163 MPa and 932 MPa,respectively,compared with 782 MPa of as-received alloy at 650℃.Also,the yield stress anomaly(YSA)occurred in SP1 and SP2 because{110}<111>and{112}<111>cross slip systems of B2 phase were difficult to slip at or below room temperature(RT),but they became active at 650℃ and above.As an essential step for increasing the spinnability of multi-pass spinning process of the Ti_(2)AlNb alloy,the H3heat treatment scheme,i.e.960℃/2 h+850℃/12 h,was carried out between two successive passes to increase the hot workability,by which the ductility of the heat treated as-spun workpieces with the microstructure of B2+primary O+acicular secondary O+high amount spheroidizedα2phases reached 72.1%at 900℃.After being subject to the H1 heat treatment scheme,i.e.960℃-2 h,the spun workpieces with the microstructure of B2+primary O+intergranular primaryα2phases achieved an optimized comprehensive mechanical properties both at room temperature and 650℃,which should be chosen as the post-spinning heat treatment process for the service requirement.