D.Y. Maeng

The effects of processing parameters on the microstructure and mechanical properties of modified B390 alloy in direct squeeze casting

Abstract The direct squeeze casting of B390 has been investigated as a function of melt temperature and applied pressure. Commercial finite volume method (FVM) computer code for heat transfer analysis, MAGMAsoft, was used to simulate cooling curves obtained from the direct squeeze casting process. The experimental and modeling results are discussed, and the correlation between cooling rate and microstructure is studied. The effects of applied pressures and melt temperature on the formation of primary Si and Chinese scripts are also discussed in connection with mechanical properties such as hardness and tensile strength.

Synthesis of tungsten monocarbide by self-propagating high-temperature synthesis in the presence of an activative additive

Tungsten monocarbide was synthesized by Self-Propagating High-Temperature Synthesis. A SHS technique was developed in this work for W-C system characterized by a low adiabatic combustion temperature of 1000 K. Samples were synthesized by in combustion wave propagating along compacts of elemental tungsten, carbon and a highly exothermal mixture [Mg + (-C2F4-)n] as an activative additive under argon atomsphere of 1 atm. A quite high conversion rate was achieved at a combustion temperature of 2109 K. It is shown that in the presence of a small amount of (about 10 wt.%) the additive mixture acquires the capacity to burn and sustain the combustion front wave propagating. The lattic of tungsten monocarbide obtained was hexagonal and its particle size was 1 ∼ 2 μm. In the final product, MgF2 and asmall amount of W2C, both byproducts, were completely removed by acidic leaching. The purity of the tungsten monocarbide was 99% after leaching.

Microstructure and mechanical properties of rapidly solidified Al-7wt.%Mg-X (X = Cr, Zr or Mn) alloys

Abstract In this study, the effect of the transition elements on the microstructure and mechanical properties of rapidly solidified Al–Mg–X alloys was investigated. As a result of the rapid solidification processing, fine equiaxed grains with a mean diameter of 2 μm were observed in these alloys. Many fine particles were found to be distributed rather homogeneously throughout the matrix with relatively big particles occasionally observed at grain boundaries. The ultimate tensile strengths of Al–Mg–X alloys were found to decrease rather remarkably at 150°C although the ductility was not increased, which may result from segregation of β(Al 3 Mg 2 ) precipitates. Fine dimples were observed on the fracture surfaces for all alloy systems and the variation of the size and shape of dimples was not observed. The ductility at 530°C was found to be ∼100%, suggesting that grain boundary sliding did not contribute despite fine grain size stabilization. The absence of superplastic behavior may be associated with low boundary misorientation in rapidly solidified Al–Mg–X alloys.

Predictions of cracking mode and hardening behavior of MMC via FEM

Abstract Finite element analyses were carried out to study the stress distribution in particulate Al 2 O 3 -reinforced Al metal–matrix composites subjected to external compressive and tensile load as a function of the interfacial bonding strength. Unit cells containing hard particles with either weak or rigid interfaces in the multi-linear kinematic hardening matrix were used to determine the corresponding flow strength. The effect of the interfacial strength on the flow response in tension and compression was also examined. The predictions of the cracking mode and hardening behavior based on FEM analyses were found to be in reasonable agreement with observations in 5083Al–10vol.% Al 2 O 3 and Al–5Mg–10vol.% Al 2 O 3 composites.

Extrusion behavior of RQ Al composite powder manufactured by a stone mill type crusher

Abstract The aim of the present investigation is to predict surface cracking and reinforcement distribution during hot extrusion in Al 6061 and 5083 composite powder reinforced by hybrid TiC–Al 2 O 3 particles. The composite powders were manufactured by crushing in the newly developed stone mill crusher using twin rolled flakes. With increasing initial billet temperature, surface cracking occurred during extrusion due to a decrease in damage criterion. It was enlightened to obtain an optimal distribution of ceramic particles in Al alloy matrix as a function of milling cycles. Optimal distribution of the reinforcement in the matrix was taken into consolidation with milling cycles.