The microstructure of the rapidly solidified foil of the hypoeutectic alloy Sn – 4.4 wt. % Zn

The article presents the results of a study of the microstructure of the rapidly solidified foil of the hypoeutectic alloy Sn – 4.4 wt. % Zn. It was found that the investigated alloy has a two-phase structure, which consists of solid solutions of tin and zinc. Doping of tin with zinc leads to a decrease in the unit cell parameter. The difference between the unit cell parameters of a rapidly solidified alloy in comparison with an alloy of pure tin tends to decrease during holding, which is due to strong supercooling of the melt during its production at ultrahigh speeds, and the formation of a supersaturated solid solution of zinc in tin, which, due to high homological temperatures, as a consequence, active diffusion processes, decomposes at room temperature. It has been established that a microcrystalline structure is formed in the foil of the alloy under study, in the cross section of which there are uniformly distributed equiaxed dispersed dark zinc precipitates against the background of a light tin matrix; the absence of zinc plates in the foil reduces the ability to brittle fracture. The unequal distribution of the average chord of random secants on the grains in the surface layers A is caused by the release of heat, which leads to a decrease in the supercooling of the subsequent layers of the melt, and an increase in the grain size as the crystallisation front moves. It was found that in the (301) plane along the [103] direction, tin twinning is observed, which occurs under the action of quenching stresses at high crystallisation rates. The alloy under study has a (100) tin texture, the formation of which is associated with the fact that the (100) plane is the most densely packed, which promotes the growth of grains with this orientation at the highest rate.

Combining Differential Scanning Calorimetry and Cooling-Heating Curve Thermal Analysis to Study the Melting and Solidification Behavior of Al-Ce Binary Alloys

Two common techniques of thermal analysis, Differential Scanning Calorimetry (DSC) and Cooling/Heating Curve Thermal Analysis (CCTA), based on different signal collected and utilizing samples with a weight difference of three orders of magnitude, were used to assess the solidification and melting behavior of Al-Ce binary alloys, containing from 5 to 20 wt. % Ce. Thermal analysis was accompanied by microscopic observations of solidified structures. For heating/cooling rates of 0.2–0.4 °C/s, temperatures of eutectic transformation L ↔ Al + Al11Ce3 in the Al-10Ce alloy along with additional proeutectic reactions L ↔ Al in the Al-5Ce hypoeutectic alloy and L ↔ Al11Ce3 in Al-15Ce and Al-20Ce hypereutectic alloys, were determined. Although there was a general agreement in major transformations, registered by DSC and CCTA during melting and solidification, differences in the reaction temperature determined exceeded the typical measurement errors for each technique. In addition, DSC and CCTA exhibited differences in detecting some proeutectic reactions and minor non-equilibrium effects, accompanying the eutectic transformation. Some factors that could contribute to differences observed and their implications for engineering practice were discussed.

Characteristics of Al-Si Alloys with High Melting Point Elements for High Pressure Die Casting

This paper is devoted to the possibility of increasing the mechanical properties (tensile strength, yield strength, elongation and hardness) of high pressure die casting (HPDC) hypoeutectic Al-Si alloys by high melting point elements: chromium, molybdenum, vanadium and tungsten. EN AC-46000 alloy was used as a base alloy. The paper presents the effect of Cr, Mo, V and W on the crystallization process and the microstructure of HPDC aluminum alloy as well as an alloy from the shell mold. Thermal and derivative analysis was used to study the crystallization process. The possibility of increasing the mechanical properties of HPDC hypoeutectic alloy by addition of high-melting point elements has been demonstrated.