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Problems of reactive diffusion at the solid phase and melt contact are studied theoretically. The rate constant is a fundamental parameter characterizing the dissolving rate at a certain configuration of experiment. Relationships between the solid phase dissolving rate, i.e. the solid phase interface boundary movement in the melt, and rates of growth of intermetallic phases in the metal (Cu) are observed. This procedure enables the creation of surface and subsurface layers of regulated thickness in metallic materials by means of reactive diffusion. The main intention was an experimental study of copper dissolving in melts of various solder alloys and the related reactive diffusion. We used Sn, SnCu, SnAgCu, SnZn and SnIn alloys as a solder material. The problems that need to be solved preferentially are emphasized. It concerns especially the determination of the rate constant of dissolving and verifying whether the proposed model equations can be used for this constant determination in cases of cylindrical and planar dissolving. Rapid growth of phases in the metal (Cu) and determination of the thickness of layers with these phases pose considerable time demands to X-ray microanalyses (WDX, EDX, BSE, SEM) of specimens after their long-time heating.

Abstract. The Sn-Zn-Al alloys are one of significant candidates in the proposal of alternative lead-free solders for higher temperature soldering. This paper deals with the study of the aluminum-tin-zinc system. Twenty Sn-Zn-Al alloys together with six binary Sn-Zn alloys were prepared and studied experimentally. Alloys were prepared from pure Sn, Zn and Al (melting and cooling in a vacuum resistance furnace). The specimens were studied metallographically including the micro-hardness measurements, complete chemical analysis (ICP-AES, OES), X-ray micro-analysis of alloys by SEM and EDX in order to determine the composition and identification of individual phases. Significant temperatures and enthalpies of phase transformations were determined by DTA. After long-term annealing of selected alloys in vacuum followed by quenching the structural and chemical microanalyses of the present phases and their limit concentrations were carried out. The achieved results were compared with the thermodynamic modelling of the ternary Sn-Zn-Al system (computer programs THERMOCALC, MTDATA, PANDAT and databases CALPHAD, COST). Electrical resistivity, density, magnetic susceptibility and wettability of Sn-Zn-Al solders were measured as well. IntroductionThe Sn-Zn-Al ternary system can be one of applicable alternative alloys to high lead content Pb-Sn solders, when the soldering process reaches temperatures as high as 300 °C. These solders can be used above all in automotive industry, in heat exchangers and in special applications. Tin -zinc alloys are used as solders for aluminum.The tin -zinc binary system diagram is of a eutectic type. The eutectic reaction proceeds at the temperature of 198.5 °C and the concentration of 85.1 at.% Sn. The zinc limit solubility in tin at this temperature corresponds to 0.6 at.% Zn, while on the other hand, the tin maximum solubility in hexagonal zinc is only 0.039 at.% Sn [1].The binary diagram of the aluminum -tin system [1, 2] is also of a eutectic type with a considerably limited solubility in the area of solid solution (Al) and tetragonal (Sn). The tin solubility in (Al) solid solution exhibits a retrograde character with a maximum of approximately 0.026 at.% Sn at the temperature of 625±20 °C [2].The Al-Zn equilibrium phase diagram [1] represents a eutectic system involving another reaction and the existence of a miscibility gap area in solid phase α (Al).The eutectic reaction proceeds at 381 °C closer to Zn side (the eutectic point corresponds to 88.7 at.% Zn). (Al) solid solution has an extended area of homogeneity interrupted at the temperature of 351.5 °C and the content of 39.5 at.% Zn. Between this temperature and the temperature of 277 °C, (Al) disintegration into two solid solutions occurs: (Al) with a lower Zn content and (Al") with a high zinc content (up to 59 at.%). The

The results of an experimental study on influence of cerium addition on structural characteristics of 42CrMo4 steel are presented. Alloying with cerium was carried out using profile filled with powdered mixture of mischmetal. The samples were taken from two ingots cast in the VHM's steelworks with standard time of casting of about 14 minutes. Three steel bars from one of the produced ingots were prepared by forging. Chemical composition, macro-and microstructure, X-ray EDX chemical microanalysis, hardness of the all steel samples were obtained. Cerium addition resulted in the formation of micrometer size inclusions which can be utilized for controlling the grain size structure of steel castings. The majority of the particles have settled at the bottom part of the casting, indicating that the convection flow during solidification was very weak. The cerium addition slightly diminished hardness of the steel. A segregation phenomenon causing inhomogeneous distribution of cerium over entire volume of as-cast samples after relatively rapid crystallization process of the steel was revealed.

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