Obtaining high-quality cast billets from Cu-Mg alloys

The technology of obtaining cast billets of the Cu-Mg (0.1–1.0%) alloys, in which continuous smelting and continuous horizontal casting are implemented in one smelting-casting aggregate, is developed. In this case, the refinement and homogenizing processing of the melt is performed continuously during the entire time of smelting and casting. Technical solutions accepted for this purpose make it possible to overcome the difficulties in providing the precision magnesium content, eliminate its strong liquation in the melt, neutralize the high surface activity of magnesium and its liability to oxidation, stabilize the recovery of magnesium from the foundry alloy and minimize the contamination of the melt by its oxidation products, attain deep removal of gases and nonmetallic inclusions from the melt, homogenize the melt in regards to the chemical composition, and acquire high-quality cast billets.     

Alloying of pseudoalloys for contact welding machine electrodes

Conclusions The alloying of W-Cu pseudoalloys with Ag results in enhancement of material properties compared to currently used commercial compositions in the W-Cu-Ni system.Use of W-Cu-Ag pseudoalloys as electrodes and clamping chucks in welding machines produces an increase in wear stability and quality of weld joints.Translated from Poroshkovaya Metallurgiya, No. 2(254), pp. 85–90, February, 1984.     

Development of RuAl-based cast alloys

Heterophase RuAl-based alloys with a β-RuAl + (1–20) vol % ɛ-Ru structure and alloyed with chromium, titanium, and hafnium are produced by vacuum arc melting. The effect of the method of preparing charge materials on their behavior during alloy formation is studied. The effect of a structure on the deformability of the alloys at room temperature is estimated. All alloys exhibit ductility and can be deformed by upsetting at a strain higher than 10–12%. The effect of deformation by upsetting at 800°C and subsequent heat treatment on the structure and properties of the alloys is investigated. The high-temperature strengths of RuAl-, TiAl-, Ni₃Al-, and NiAl-based alloys are compared by measuring their hot hardnesses at temperatures up to 1100°C. The high-temperature strength characteristics of the RuAl-based alloys are higher than those of the Ni3Al-, TiAl-, and NiAl-based alloys over the entire temperature range under study; at temperatures ≥900°C, the hardness of ruthenium monoaluminide is higher than those of the other alloys by a factor of 2–4.     

Microsegregation in unidirectionally cast copper alloys

Solute concentrations in dilute Cu-Ni, Cu-Ag, and Cu-Sb alloys have been measured at the centers of primary and secondary dendrites and in the interdendritic regions, using electron probe microanalysis. It was found that in the Cu-Ni alloys, the segregation ratio was independent of distance from the chill and alloy composition, with the effective distribution coefficient differing significantly from the equilibrium value. In the Cu-Ag and Cu-Sb alloys the segregation ratio was markedly dependent on distance from the chill and alloy composition, being greatest farthest from the chill. The microsegregation associated with secondary dendrite branches differs from that of the primary branches for the same spacing, the amount depending on the system. One ternary alloy, Cu-Ag-Ni, was examined and it was demonstrated that the presence of a second solute markedly influenced the microsegregation of the first solute. Measurements were made of primary and secondary dendrite arm spacing in the castings for increasing distances from the chill. The spacings are considered in terms of pouring temperature, freezing rate, and cooling rate. It was found that, in general, no simple relationship existed between dendrite spacing and the above variables within the range of conditions investigated in this study. Solute distributions across individual primary dendrite stalks were determined and related to curves calculated on the basis of complete mixing and diffusion solute transport in the liquid. For the Cu-Ag and Cu-Sb alloys(k < 1), good agreement was obtained between the experimental and complete mixing curves, using an effective value fork in the calculations determined from the dendrite center concentrations. For the Cu-Ni alloys(k > l), only a part of each experimental curve could be fitted by either the complete mixing or diffusion transport calculated curves.     

Capillary welding of sintered hard alloys

Conclusions The processes occurring during the welding of hard alloys are analyzed, and a mechanism describing the filling of the contact gap with molten cobalt is proposed. Suitable process parameters are recommended for the manufacture of hard-alloy parts by the welding technique.Translated from Poroshkovaya Metallurgiya, No. 8 (128), pp. 28–33, August, 1973.     

Al-Zn-Mg-based cast alloys having high mechanical properties

The effect of alloying elements and heat treatment on the structure and properties of cast alloys based on the Al-Zn-Mg system and containing more than 9% (Zn + Mg) is analyzed. The optimum chemical composition of an alloy from this system is determined, and the heat-treatment conditions required for improving the mechanical properties of the alloy are found.     

Modeling high-temperature stress-strain behavior of cast aluminum alloys

A modified two-state-variable unified constitutive model is presented to model the high-temperature stress-strain behavior of a 319 cast aluminum alloy with a T7 heat treatment. A systematic method is outlined, with which one can determine the material parameters used in the experimentally based model. The microstructural processes affecting the material behavior were identified using transmission electron microscopy and were consequently correlated to the model parameters. The stress-strain behavior was found to be dominated by the decomposition of the metastable θ′ precipitates within the dendrites and the subsequent coarsening of the θ phase, which was manifested through remarkable softening with cycling and time. The model was found to accurately simulate experimental stress-strain behavior such as strain-rate sensitivity, cyclic softening, aging effects, transient material behavior, and stress relaxation, in addition to capturing the main deformation mechanisms and microstructural changes as a function of temperature and inelastic strain rate.     

Fluidized bed heat treatment of cast Al-Si-Cu-Mg alloys

The effects of fluidized bed heat treatment on the microstructural and mechanical properties of Al-Si-Cu-Mg cast alloys, namely, 354 and 319, were studied. The heating rate in fluidized beds (FBs) is greatervis-à-vis conventional electrical resistance furnaces (CFs). The high heating rate in FBs increases the kinetics of metallurgical phenomena such as Si fragmentation and spherodization during solution heat treatment, as well as the precipitation rate of phases such as Al₅Cu₂Mg₈Si₆ and Al₂Cu during aging. It is observed that the dissolution rate of phases such as Mg₂Si and Al₅Cu₂Mg₈Si₆ takes place very rapidly. The solution heat treatment of 319 alloy using FB results in complete dissolution of Mg₂Si and Al₅Cu₂Mg₈Si₆ particles within 45 minutes. However, for phases such as Al₂Cu and Ferich intermetallics, the dissolution rate is relatively slow. Even on prolonged solution heat treatment for 6 hours, these phases do not dissolve completely. It is observed that incomplete dissolution of the Al₂Cu phase does not significantly affect tensile properties of T4-treated alloys. The optimum solution heat-treatment time in FB for both 354 and 319 alloys is 45 minutes at 527 °C and 493 °C, respectively. Thermal analysis shows an exothermic peak owing to recrystallization and coarsening of eutectic grains during solution heat treatment. The high heating rate in FB causes this transformation to take place at a lower temperature than in CF. It is observed that the nucleation rate of Al₅Cu₂Mg₈Si₆ during aging in FB is greater than using CF. Thermal analysis of samples during the ramp-up stage while aging using FB did not show any phase transformation, while those using CF show two endothermic transformations, which are most likely due to the dissolution of GP zones or the co-cluster of solutes. Aging at 200 °C results in a greater number density of precipitates than those at 240 °C. The tensile strength of samples aged at 200 °C is greater than those aged at 240 °C, because the amount of precipitates formed at 200 °C is greater than that at 240 °C. The total heat-treatment time for T6 temper is less than 2 hours in FBs, which is a significant reduction in heat-treatment time, as well as energy consumption.     

A statistically significant experimental technique for investigating microsegregation in cast alloys

A simple, statistically significant experimental technique was developed to investigate microsegregation in a model cast Al-4.5 wt pct Cu alloy. This technique involves systematic composition measurements of the primary alloy phase of polished samples by use of the electron microprobe. The microprobe data were processed to obtain the detailed compositionvs fraction solid profile, which was an estimation of microsegregation of solute element in the sample. The number of data collected directly affected the statistical significance of the results. The results suggested that measurements of the order of 100 are adequate for obtaining statistically significant solute distribution profiles and, hence, for quantitatively determining the severity of microsegregation.     

Electron-beam welding behavior in Mg-Al-based alloys

The electron-beam welding (EBW) behaviors of pure Mg and the AZ31, AZ61, and AZ91 Mg alloys are examined in this study, in terms of fusion-zone characteristics, grain structures, texture evolution, and joint efficiency. With increasing A1 content, the Mg-based materials were found to be more easily fusion welded. The AZ91 alloy could be welded using a beam power of 2200 W and a weld speed of 16 mm/s, resulting in a weld depth of 29 mm with a fusion-zone aspect ratio of 8.2. The grains inside the fusion zone were nearly equiaxed in shape and ∼10 μm in size, due to the rapid cooling rate. Extended partial melting zones were observed in alloys with high solute contents, such as AZ61 and AZ91. The postweld tensile strength of the Mg alloys could recover back to ∼80 to 110 pct of the original strength. The texture in the fusion zone was traced by X-ray diffraction (XRD) and electron-backscattered diffraction (EBSD). The grain orientations inside the rapidly solidified electron-beam-welded fusion zones are still rather diversely distributed. The α ₁-, α ₂-, and α ₃-axes of some grains tend to align at 90 or 30 deg with respect to welding direction, and the c-axis tends to align along the plate normal direction. The influence from surface tension on the weld top-surface appearance and weld depth was not pronounced for the current four Mg materials. Instead, differences in the solidus temperatures and thermal conductivity should be the primary factors.