Microstructural Characterization and Mechanical Properties of VB_2/A390 Composite Alloy

In this work, we make the best use of the vanadium element; a series of A1-V-B alloys and VB2/A390 composite alloys were fabricated. For Ak-10V-6B alloy, the grain size of VB2 can be controlled within about 1 μm and is distributed uniformly in the AI matrix. Further, it can be found that VB2 promises to be a useful reinforcement particle for piston alloy. The addition of VB2 can improve the mechanical properties of the A390 composite alloys significantly. The results show that with 1 % VB2 addition, A390 composite alloy exhibits the best performance. Compared with the A390 alloy, the coefficient of thermal expansion is 13.2 × 10^-6 K-1, which decreased by 12.6%; the average Brinell hardness can reach 156.5 HB, wear weight loss decreased by 28.9% and ultimate tensile strength at 25℃ （UTS25 ℃） can reach 355 MPa, which increased by 36.5%.

Surface alloying of Al films/Ti substrate based on high-current pulsed electron beams irradiation

Ti–Al surface alloy was fabricated using a cyclic pulsed liquid-phase mixing of predeposited 100 nm Al film with a-Ti substrate by low-energy high-current electron beam. Electron probe micro-analysis（EPMA）,grazing incidence X-ray diffraction analysis（GIXRD）,transmission electron microscopy（TEM）, and nanoindentation were used to investigate the characterization of Ti–Al surface alloy. The experimental results show that the thickness of alloy layer is ＊3 lm, and the content of Al in the ＊1 lm thickness surface layer is ＊60 at%. The tetragonal TiAl and TiAl2intermetallics were synthesized at the top surface, which have nanocrystalline structure.The main phase formed in the ＊2.5 lm thick surface is TiAl, and there are few TiAl2and Ti3Al phase for the alloy.Dislocation is enhanced in the alloyed layer. The nanohardness of Ti–Al surface alloy increased significantly compared with a-Ti substrate due to the nanostructure and enhanced dislocation. Since the e-beam remelted repeatedly, the Ti–Al surface alloy mixed sufficiently with Ti substrate. Moreover, there is no obvious boundary between the alloyed layer and substrate.

Effects of Cooling Rate and Component on the Microstructure and Mechanical Properties of Mg–Zn–Y Alloys

The microstructure and mechanical properties of Mg–6Zn–1Y and Mg–6Zn–3Y（wt%） alloys under different cooling rates were investigated. The results show that the second dendrite arm spacing（SDAS） of Mg–6Zn–1Y and Mg–6Zn–3Y is reduced by 32 and 30% with increasing cooling rates（Rc） from 10.2 to 23 K/s, which can be predicted using a empirical model of SDAS=68 R 0：45：45cand SDAS=73 R 0c, respectively. The compressive strength of both alloys increases with increasing the cooling rate, which is attributed to the increase of volume fraction（Vf） of secondary phases under high cooling rate. The interaction of the cooling rate and component with SDAS has been theoretically analyzed using interdependence theory.

Microstructure and Mechanical Properties of Galvanized Steel/AA6061 Joints by Laser Fusion Brazing Welding

Laser fusion brazing welding was proposed.Galvanized steel/AA6061 lapped joint was obtained by laser fusion brazing welding technique using the laser-induced aluminium molten pool spreading and wetting the solid steel surface.Wide joint interface was formed using the rectangular laser beam coupled with the synchronous powder feeding.The result showed that the tiny structure with the composition of a-Al and Al–Si eutectic was formed in the weld close to the Al side.And close to the steel side,a layer of compact Fe–Al–Si intermetallics,including the Al-rich FeAl3,Fe2Al5 phases and Al–Fe–Si s1 phase,was generated with the thickness of about 10–20 lm.Transverse tensile shows the brittlefractured characteristic along to the seam/steel interface with the maximum yield strength of 152.5 MPa due to the existence of hardening phases s1 and Al–Fe intermetallics.

Microstructure Evolution and Mechanical Properties of a SMATed Mg Alloy under In Situ SEM Tensile Testing

Surface mechanical attrition treatment（SMAT） has been recently applied to bulk polycrystalline magnesium（Mg） alloys with gradient grain size distribution from the impact surface to inside matrix, hence effectively improving the alloys＇ mechanical performances. However, in-depth understanding of their mechanical property enhancement and grain size-dependent fracture mechanism remains unclear. Here,we demonstrated the use of in situ micro-tensile testing inside a high resolution scanning electron microscope（SEM） to characterize the microstructure evolution, in real time, of SMATed Mg alloy AZ31 samples with different grain sizes of ~10 μm（＇coarse-grain sample＇） and ~5 μm（＇fine-grain sample＇）, respectively, and compared the results with those of a raw Mg alloy AZ31. The quantitative tensile tests with in situ SEM imaging clearly showed that fracture of ‘fine-grain sample＇ was dominated by intergranular cracks,while both trans-granular and intergranular cracks led to the final failure of the ‘coarse-grain samples＇.It is expected that this in situ SEM characterization technique, coupled with quantitative tensile testing method, could be applicable for studying other grain-refined metals/alloys, allowing to optimize their mechanical performances by controlling the grain sizes and their gradient distribution.

Improving the Hydromechanical Deep-Drawing Process Using Aluminum Tailored Heat Treated Blanks

The present work demonstrates the effectiveness of combining the hydromechanical deep-drawing process with the Tailored Heat Treated Blank（THTB） technique. In the hydromechanical deep-drawing process, the fluid pressure is used for postponing the fracture occurrence in the blank, while the THTB technique allows to create a material property gradient through a suitable artificial aging treatment carried out prior to the forming process. Since the number of process variables is large, in the present work the authors propose an optimization loop for the determination of the parameters controlling the extension of the blank regions to be subjected to the aging treatment and the temperature levels to be set during the heat treatment. The proposed methodology couples a simple finite element model（Abaqus） with a multiobjective optimization platform（mode FRONTIER）. A preliminary experimental campaign was carried out for determining the effect of the aging treatment on the mechanical（through tensile tests） and deformative（through formability tests）behavior of the AC170 PX aluminum alloy. Optimization results prove the effectiveness of the adopted methodology and put in evidence that the adoption of properly aged blanks in the hydromechanical deep drawing allows to increase the limit drawing ratio and to simplify the process since it is conducted at room temperature.