Influence of High-Speed Milling Process on Mechanical and Microstructural Properties of Ultrafine Grained Profiles Produced by Linear Flow Splitting

The effects of milling parameters on the surface quality,microstructures and mechanical properties of machined parts with ultrafine grained(UFG)gradient microstructures are investigated.The effects of the cutting speed,feed per tooth,cutting tool geometry and cooling strategy are demonstrated.It has been found that the surface quality of machined grooves can be improved by increasing the cutting speed.However,cryogenic cooling with CO_2 exhibits no significant improvement of surface quality.Microstructure and hardness investigations revealed similar microstructure and hardness variations near the machined groove walls for both utilized tool geometries.Therefore,cryogenic cooling can decrease more far-ranging hardness reductions due to high process temperatures,especially in the UFG regions of the machined parts,whilst it cannot prevent the drop in hardness directly at the groove walls.

Enhanced Strength-Ductility Synergy in Submerged Friction Stir Processing ER2319 Alloy Manufactured by Wire-Arc Additive Manufacturing via Creating Ultrafine Microstructure

Submerged friction stir processing(SFSP)with flowing water was employed to alleviate the porosities and coarse-grained structure introduced by wire-arc manufacturing.As a result,uniform and ultrafine grained(UFG)structure with average grain size of 0.83μm was achieved with the help of sharply reduced heat input and holding time at elevated temperature.The optimized UFG structure enabled a superior combination of strength and ductility with high ultimate tensile strength and elongation of 273.17 MPa and 15.39%.Specifically,grain refinement strengthening and decentralized θ(Al_(2)Cu)phase in the sample subjected to SFSP made great contributions to the enhanced strength.In addition,the decrease in residual stresses and removal of pores substantially enhance the ductility.High rates of cooling and low temperature cycling,which are facilitated by the water-cooling environment throughout the machining process,are vital in obtaining superior microstructures.This work provides a new method for developing a uniform and UFG structure with excellent mechanical properties.

Strengthening contributions in ultra-high strength cryorolled Al-4%Cu-3%TiB_2 in situ composite

Ultra-high strength Al alloy system was developed by cryorolling and the contribution of various strengthening mechanisms to the overall yield strength of the system was evaluated. Cryorolling of Al-4%Cu-3%TiB2 in situ composite followed by short annealing at 175 ℃ and ageing at 125℃ resulted in an ultra-high yield strength of about 800 MPa with 9%total elongation. The strengthening contributions form solid solution strengthening, grain refinement, dislocation strengthening, precipitation hardening and dispersion strengthening were evaluated using standard equations. It was estimated that the maximum contribution was from grain refinement due to cryorolling followed by precipitation and dispersion strengthening.

Corrosion behavior of hypereutectic Al-23%Si alloy (AC9A) processed by severe plastic deformation

Ultrafine-grained(UFG) hypereutectic Al-23%Si (mass fraction) alloy was achieved through equal-channel angular pressing(EACP) procedure. And the electrochemical properties after various ECAP passes were investigated in neutral NaCl solution. Potentiostatic polarization curves show that the corrosion potential of the ECAPed sample after 4 passes decreases markedly, while the corrosion current density reaches 1.37 times that of the as-cast alloy. However, the φcorr and Jcorr values after 16 passes are improved and approach those of the as-cast alloy. Immersion tests also show that the mass-loss ratio of ECAPed alloy decreases with increasing the pressing pass, which is lowered to 28.7% with the increase of pass number from 4 to 16. Pitting susceptibility of the ECAPed alloy after initial 4 passes is boosted, due to the presence of biggish voids resulted from the breakage of brittle large primary silicon crystals during ECAP. Increasing ECAP pass makes the voids evanesce and results in the homogeneous ultrafine-grained structure, contributing to a higher pitting resistance. These results indicate that enough ECAP passes are beneficial to increasing corrosion resistance of the hypereutectic Al-23%Si alloy.

Interface Microstructure of Al-Fe Tubes Joint by Magnetic Pulse Welding

Magnetic Pulse Welding(MPW)is a very high speed process which produces solid-state welds.In this work, Welding interface microstructure of Al/Fe tubes by MPW and its influence factors were investigated.The equipment with a capacitor of 100 μF was used under different voltages range from 8 kV to 15 kV.SEM and TEM observation were carried out to investigate microstructure of the welding interface.The results show that the dissimilar tubes(Al/Fe)could be welded with the optimum tapered angle of about 4 degree.The welding interface in Al/Fe joints exhibits a characteristic wavy morphology with wavelength of about I00 μm.A new layer exists between base tubes consisting of AI and Fe elements.Ultrafme grained microstructure is founded near the welding interface.The results obtain in this work provide the fundamentals for the investigation of MPW mechanism of dissimilar tubes.