Microstructural characteristics and mechanical behavior of B4Cp/6061Al composites synthesized at different hot-pressing temperatures

B4Cp/6061Al composites have become important structural and functional materials and can be fabricated by powder metallurgy and subsequent hot rolling. In this work, the effects of the hot-pressing temperature on microstructures and mechanical behaviors of the B4Cp/6061Al composites were investigated. The results showed that compared with the T4 heat treated B4Cp/6061Al composite hot pressed at 560℃, the yield strength and failure strain of the composites hot pressed at 580℃ were increased to 235 MPa and 18.4%, respectively. This was associated with the interface bonding strength between the B4C particles and the matrix. However, the reaction products, identified to be MgAl2O4 phases, were detected in the composites hot pressed at 600℃. The formation of the MgAl2O4 phases resulted in the Mg depletion, thus reducing the yield strength to 203.5 MPa after the T4 heat treatment due to the effect of the solid solution strengthening being weakened. In addition, the variation of hardness and electrical conductivity was mainly related to the Mg content in the matrix. Based on the as-rolled microstructures observed by SEM, SR-μCT and fracture surfaces, the deformation schematic diagram was depicted to reflect the tensile deformation process of the composites.

Enhancing mechanical properties and corrosion resistance of nickel-aluminum bronze via hot rolling process

The mechanical properties and corrosion behavior of as-cast, as-annealed and hot-rolled nickelaluminum bronze(NAB) alloy(Cu-9 Al-10 Ni-4 Fe-1.2 Mn, all in wt.%) in 3.5 wt.% Na Cl solution were investigated. The results show that annealing introduces a large number of k phases to precipitate in the k phase. However, after further hot rolling, the original continuous k phases are spheroidized and dispersed, increasing the strength, hardness, and elongation of the alloy. In addition to the enhanced mechanical properties, the corrosion resistance of the NAB samples is also improved significantly by hot rolling, as revealed by the mass loss measurements, electrochemical impedance spectroscopy(EIS), and cross-sectional corrosion morphology. Selective phase corrosion occurs by the preferential corrosion of the k phase, which acts as an anode to the k phases, and the uncorroded k phases are retained in the corrosion product film. The interfaces between the k phases and the surrounding corrosion products become discontinuous caused by the spheroidization of k phases, reducing the corrosion of the substrate by the corrosive medium via the channels. As a result, the corrosion rate and the maximum local corrosion depth of the hot-rolled NAB sample are greatly reduced.

Microstructural evolution and strengthening mechanism of Al–Mg alloys with fine grains processed by accumulative continuous extrusion forming

In this work,the mechanical properties and strengthening mechanisms induced by microstructural evolution in a rheo-extruded 5087 alloy processed via accumulative continuous extrusion forming(ACEF)were investigated.Electron back-scattered diffraction(EBSD)and transmission electron microscopy(TEM)were utilized to characterize the microstructure of the alloy subjected to ACEF with various passes.The grain refinement caused by continuous dynamic recrystallization(CDRX)was discussed.The results demonstrated that after 3 passes of ACEF,there was a significant grain refinement effect on the alloy,and the average grain size decreased from 45.6μm to 2.5μm;the ultimate tensile strength(UTS)and yield strength(YS)of the alloy increased to 362.8 MPa and 234.6 MPa,respectively.Dislocation cells/walls generated during deformation promoted the formation of low angle grain boundaries(LAGBs).The accumulative strain accelerated the transformation of LAGBs to high angle grain boundaries(HAGBs).Dislocation pile-up enhanced the driving force of CDRX,and nano-sized Al_6(Mn,Fe)phases at the grain boundaries inhibited the growth of grains due to the pinning effect.Based on the quantitative estimation,dislocation strengthening and grain boundary strengthening dominated the enhancement in YS of the ACEFed alloy.

Quantitative mechanisms behind the high strength and electrical conductivity of Cu-Te alloy manufactured by continuous extrusion

The microstructure,mechanical performance,and electrical conductivity of Cu-Te alloy fabricated by continuous extrusion were quantitatively investigated.The results demonstrate that the grain size of the Cu-Te alloy is refined significantly by incomplete dynamic recrystallization.The Cu2Te phase stimulates recrystallization and inhibits subgrain growth.After extrusion,the tensile strength increases from217.8±4.8 MPa to 242.5±3.7 MPa,the yield strength increases from 65.1±3.5 MPa to 104.3±3.8 MPa,and the yield to tensile strength ratio is improved from 0.293±0.015 to 0.43±.0.091,while the electrical conductivity of room temperature decreases from 95.8±0.38%International Annealed Cu Standard(IACS)to 94.0%±0.32%IACS.The quantitative analysis shows that the increment caused by dislocation strengthening and boundary strengthening account for 84.6%of the yield strength of the extruded Cu-Te alloy and the electrical resistivity induced by grain boundaries and dislocations accounts for 1.6%of the electrical resistivity of the extruded Cu-Te alloy.Dislocations and boundaries contribute greatly to the increase of yield strength,but less to the increase of electrical resistivity.