Effect of the initial ECAP passes on crystal texture and residual stresses of 5083 aluminum alloy

To produce a highly refined microstructure,several metals or alloys have been processed via equal-channel angular pressing(ECAP).In this work,the mechanical and microstructural changes of the 5083 aluminum alloy in H11 condition after processed by two ECAP passes were investigated.An ECAP H13 steel die with an inner angle(α)of 120°and outer curvature(β)of 20°was used.The microstructural changes were associated with the loss of texture symmetry.The morphologies of the Mg2Si andα-Al(Mn,Fe)Si precipitates for the sample at the initial condition were similar to those subjected to two ECAP passes.The peak broadening measured by X-ray diffraction revealed an increment of both grain refinement and microstrain.After the second extrusion pass,the hardness increased by 62%compared with the initial condition.Moreover,the heterogeneous hardness behavior was compatible with a highly localized dislocation density.After two ECAP passes,shear parallel bands were observed to be at nearly 45°to the extrusion direction.The evaluation of first-order residual stress as a function of the depth of the analyzed sample displayed compressive or tensile values,depending on the measured face.With the plastic deformation applied,the first and second-order residual stresses exhibited significant increment.Williamson-Hall plots showed positive slopes,indicating an increment in the microstrain.

Glass formation,thermal and mechanical properties of ZrCuAlNi bulk metallic glasses

The glass forming ability, thermal and mechanical properties of some Zr Cu Al Ni bulk metallic glasses were analyzed. The compositions of the alloys were theoretically determined with the dense packing and kinetic fragility index models. Cylindrical and conical ingots were produced by copper mould suction-casting under Ar atmosphere. The conical ingots were characterized by means of X-ray diffraction in order to determine the glassy structure. It was found that both alloys have a critical glassy diameter, Dc, of 3 mm. Thermal behaviours were investigated by differential scanning calorimetry at heating rates of 0.5, 0.67 and 0.83 K/s. The gamma parameter γ, supercooled liquid region ΔTx, and reduced glass transition temperature Trg, of the experimentally obtained glasses indicated high glass forming ability. The glassy compositions showed a fragility index of ~40 GPa. The compression test of the investigated alloys was carried out at a strain rate of 0.016 s^-1, obtaining a elastic modulus of ~83 GPa, total deformation of ~5%, yield strength of 1.6 GPa and hardness of 4 GPa. It was concluded that the use of the dense packing and kinetic fragility index models helped to predict glass-forming compositions in the family alloy investigated.

Synthesis and characterization of bulk composite Fe-Si-B alloys with small concentration of Nb and Mo

The preparation and some mechanical, thermal and magnetic properties of the as cast bulk composite Fe72B19.2Sin.sM4 （M=Nb, Mo） alloys obtained by suction casting are presented and discussed. The microstructrural results showed the existence of a crystalline a-Fe（Si） phase embedded in a glassy matrix. The values of microhardness （/Iv） and yield strength （ay） for the Nb-containing alloy are exceptionally high, i.e. （12.65~0.3） GPa and （4.22~0.10） GPa, respectively. The saturation polarization values are found to be as high as 1.24 T for both composite ~11oys. It is thought that the interplay between the secondary crystalline phases and amorphous matrix could be responsible for the mechanical and magnetic behaviour of these alloys.

Hardness-Lattice Parameter Correlation for Aged Al-Zn-Mg Alloys

Two ternary Al-2.2Zn-0.95Mg and Al-5.SZn-2.1Mg （in wt pct） alloys, with Zn：Mg ratios close to 2.5 were produced by conventional ingot casting metallurgy. The ingots were solution heat treated at 500℃ for 0.5 h and aged at 180℃ for times between 0.5 and 80 h. The structural characterization was carried out by X-ray diffraction （XRD）, transmission electron microscopy （TEM）, selected area electron diffraction （SAED） and Vickers mierohardness measurements （HV）. The study was focused on the investigation of the precipitates formation and the relationship between hardness and lattice parameter for α-Al. The results showed that there was an inverse correlation for all the experimental conditions, and the aged peaks coincided with lattice parameter minima. Significant precipitates formation only occurred for the alloy containing 5.5 wt pct Zn and 2.1 wt pct Mg, provoking an important strengthening and variations in the lattice parameter, however, this was not observed for the alloy containing 2.2 wt pct Zn and 0.95 wt pct Mg. A plausible explanation of the increment of hardness values could be the presence of a well distributed η phase （MgZn2）. At initial stages of the precipitation process, η′ was the most abundant precipitate while the phase τ- was observed at overaged conditions. These results showed that the aging response of the conventionally cast Al-Zn-Mg alloys could be obtained using the lattice parameter of the α-Al matrix, even for alloy systems with low precipitates formation.