Влияние высоких давлений на формирование новых соединений в сплаве Al-=SUB=-86-=/SUB=-Ni-=SUB=-2-=/SUB=-Со-=SUB=-6-=/SUB=-Gd-=SUB=-6-=/SUB=--=SUP=--=SUP=-*-=/SUP=--=/SUP=-

The structure, elemental and phase composition of the eutectic alloy Al86Ni2Со6Gd6 (hereinafter referred to as at.%) During the solidification of the melt from 1500oC at a rate of 1000oC/s under high pressure of 3 and 7 GPa have been investigated by X-ray diffraction analysis and electron microscopy. Solidification of the melt under high pressure leads to a change in the phase composition of the alloy and the formation of an anomalously supersaturated solid solution of α-Al (Gd). At a pressure of 7 GPa, new phases were synthesized: Al3Gd * (like Al3U) containing Co and Ni, with a primitive cube structure (cP4/2) with a lattice parameter a = 4.285 ± 0.002 Angstrem and Al8Co4Gd * (like Al8Cr4Gd) with a tetragonal structure (tI26/1) with parameters a = 8.906 ± 0.003 Angstrem and c = 5.150 ± 0.003 Angstrem. The structure of all the samples obtained is homogeneous, dense, finely dispersed, without shrinkage cavities and pores. The average microhardness of the samples is high due to solid solution and precipitation hardening.

A Review Study on the Main Sources of Porosity in Al-Si Cast Alloys

The present study was performed on A356 and B319 alloys in mechanically stirred or degassed condition. Melts were Sr-modified and grain-refined. Hydrogen content was varied from less than 0.1 ml/100 g Al to ∼0.4 ml/100 g Al; Fe was increased to 0.8% in B319 alloy. Lanthanum and cerium were added as 99.5% pure metals. Two main techniques were used to investigate porosity formation: fracture surface of tensile or fatigue test bars, or reduced pressure test (RPT) method. Porosity type and shape were examined. The results show that pore size is more influential than small scattered ones from a mechanical point of view. Tensile testing is affected by porosity located at the center of the testing bar, whereas edge porosity is responsible for crack initiation in case of fatigue testing. Intermetallics precipitate in the form of intercepted platelets which restricts the flow of the molten metal, leading to formation of shrinkage cavities. Precipitation of clusters of compounds from the liquid state such as Al2Si2Sr, Mg2Sn, Al3Ti, or added Al2O3particles would as well act as nucleation sites for porosity formation. Most oxides were observed in the form of long branched strings. In some cases, bifilms were also reported in addition to SrO and MgO.

Influence of differential reduction rate in adjacent roll reduction zone on internal cracks of high carbon bloom induced by mechanical soft reduction

To comprehensively investigate and alleviate internal cracks in high carbon bloom induced by mechanical soft reduction (MSR), a 3D thermal-mechanical coupled model, containing two adjacent pairs of reduction rolls, was developed to investigate the influence of differential reduction rate on evolution of stress concentration and displacement in as-cast bloom. In order to effectively provide theoretical basis for actual production, the reduction rate was calculated according to the appropriate reduction amount of each pair of reduction rolls, which can be adopted in the MSR to determinate the appropriate roll reduction amount in adjacent roll reduction zone. With the differential reduction rate of MSR increasing from −2.67 mm/m to 5.33 mm/m, the maximum equivalent stress of cracking area in as-cast bloom significantly decreased under first roll reduction position, the maximal displacement along the bloom width direction is significantly decreased with increasing of the differential reduction rate of MSR under end roll reduction position. According to the results of industrial experiment, the internal cracks were effectively alleviated and center shrinkage cavities were nearly eliminated by optimum designed experiments.

Production of Primary Silumins Ingots Modified with Strontium

The article examines a number of regularities in the production of primary cast ingots of AlSi7Mg, AlSi7MgSr, AlSi11Mg, and AlSi11MgSr. Peculiarities of melting and cast of these alloys, as well as the effect silicon and strontium have on the formation of the shrinkage cavities, have been explored. It has been demonstrated that strontium, when used as a modifier, changes not only the morphology of silicon, but also the nature of solidification and shrinkage of the alloy. Defects formed in the ingots manufactured from near – eutectic AlSi11MgSr alloy have been studied in greater detail.

Analysis of internal cracks in high carbon casting bloom induced by soft reduction process and its improvement using numerical simulations and industrial experiments

To comprehensively investigate and improve the internal cracks in high carbon casting bloom induced by the soft reduction process, a three-dimensional mechanical model was developed to calculate the cracking zone, centre solid fraction and the strain states in as-cast bloom. In the present work, the specific relationship between cracking zone area, centre solid fraction and maximum equivalent strain in cracking zone has been established under a number of withdrawal machines. A two-stage sequential soft reduction method was carried out for high carbon bearing steel, which aims to provide theoretical basis for improving the internal quality and effectively decrease the risk of internal cracks. According to the experimental results, the internal cracks were effectively alleviated and center shrinkage cavities were nearly eliminated by optimum designed experiments. Along the bloom central part, the proportion of length where the segregation rate is between 0.95 and 1 has been increased from 16.7% to 91%, and the fluctuation of carbon distribution in the center line of as-cast bloom was decreased to obtain the high homogeneity of the internal structure. In addition, grade of banded carbide in the hot-rolled wire decreased accordingly from 2.5 to 1.67.

Influence of Specific Energy on Microstructure and Properties of Laser Cladded FeCoCrNi High Entropy Alloy

Specific energy is a key process parameter during laser cladding of high entropy alloy (HEA); however, the effect of specific energy on the microstructure, hardness, and wear resistance of HEA coating has not been completely understood in the literature. This paper aims at revealing the influence of specific energy on the microstructure and properties of laser cladded FeCoCrNi high entropy alloy on the Ti6Al4V substrate, and further obtains feasible process parameters for preparation of HEA coating. Results indicate that there are significant differences in the microstructure and properties of the coatings under different specific energy. The increase of specific energy plays a positive role in coarsening the microstructure, promoting the diffusion of Ti from the substrate to HEA coating, and subsequently affects the hardness of samples. The HEA coating is mainly composed of the face-centered cubic phase and body-centered cubic phase, precipitating a small amount of Fe-Cr phase and Laves phase. Metallurgical bonding is obtained between the base metal and the coatings of which the bonding region is mainly composed of columnar crystal and shrinkage cavities. The microhardness of the HEA coating reaches 1098 HV, which is about 200% higher than that of the TC4 substrate, and the wear resistance is significantly improved by the HEA coating.

Effect of Moisture Content of Green Sand on The Casting Defects

In this study, three percentages of moisture content on the green sand were benchmarked to be observed their effects on the casting defects. The metal used is scrap Al-Si with wt% of Al 59.7. The metal was melted in a furnace at 550 ºC then poured into sand molds and cooled for 24 hours before it can be removed, cleaned, and finished. There were prepared three specimens for each benchmark. Qualitative observation of defects was done by physical observations on the surface of the specimens. The observations show that on the moisture content of 2.5%, there is a defect in the form of porosity. Defects in the form of drops, misruns, blowholes, and shrinkage cavity are found on the benchmark 3.5%. The most severe defects are found on the benchmark 4.5% in the form of buckles and severe shrinkage cavities that are found in almost all specimens.