The paper presents the results from a study on the impact of the cooling rate in the eutectoid transition on the abrasive wear of the as cast Zn-4Al alloy. The microstructure of the researched material consists of dendrites of the η solid solution and an (α+η) eutectic structure. During the eutectoid transformation at 275oC the distribution in the eutectic structure was transformed and fined. Heat treatment was carried out for this alloy, during which three cooling mediums were used, i.e. water, air and an furnace. For the research material obtained in this way, metallographic examinations were performed using the methods of light and scanning electron microscopy, as well as hardness measurements. It was found that faster cooling rate promoted the fragmentation of structural components, which translates into higher hardness of the material. This also had effects in the tribological wear of the tested alloy. As part of the tests, an abrasive wear test was carried out on a standard T-07 tester.

The paper presents the research results of the solenoid housing made of the Zn4Al1Cu alloy that was destroyed as a result of corrosion.

Surface of the tested part showed macroscopically the features typical for white corrosion, and the resulting corrosion changes led to a

disturbance of the alloy cohesion. The research performed have shown that the tested solenoid valve has intergranular corrosion as a

reaction of the environment containing road salt. The corrosion was initiated in the areas of the alfa phase existence appearing in the

eutectic areas which propagated over dendritic areas of the alloy. Initiation of the corrosion followed as a result of the galvanic effect of

the alfa phase reach in aluminium showing higher electrochemical potential, in contact with the eta phase reach in zinc. The impact of the

phase reach in lead present in the microstructure on the corrosion processes run was not found.

In this work, the effect of the microstructure on corrosion behavior of selected Mg- and Al-based as cast alloys, was evaluated. The electrochemical examinations were carried out, and then a morphology of corrosion products formed due to local polarization on materials surface, was analyzed. It was documented that the presence of Mg2Si phase plays an important role in the corrosion course of Mg-based alloy. A selective etching was observed in sites of Mg2Si precipitates having “Chinese script”- like morphology. Analogous situation was found for Al-based alloy, where the key role was played by cathodic θ-CuAl2 phase.

Cold spraying as a low-temperature coating deposition method is intended for thermally sensitive materials. Due to its precise temperature control, it limits the formation of structural defects, and can therefore be easily applied to spray corrosion protective coatings made from metal or metal-ceramic powders. However, the formation of pure ceramic coatings with the use of cold spraying is still not so common. Titanium dioxide is one of the most interesting ceramics due to its photocatalytic properties. Nevertheless, these types of coating materials usually work in a corrosion favoring humid atmosphere. In the presented paper, amorphous TiO2 powder was deposited onto aluminum alloys and steel substrates and then submitted to potentiodynamic corrosion tests in a 3.5 wt.% NaCl solution. The as-sprayed coating showed phase transition from amorphous TiO2 to anatase, and also revealed porosity. As a result, electrolytes penetrated the coating and caused undercoating corrosion in the tested environment of an aqueous NaCl solution. The analysis of the potentiodynamic curves showed that the presence of the coating decreased corrosion potential on both substrates. It arose from the mixed phases of TiO2, which consisted of photocathode – amorphous material and photoanode – crystalline anatase. The phase mixture induced the galvanic corrosion of metallic substrates in the presence of electrolytes. Moreover, pitting-like corrosion and coating delamination were detected in aluminium alloy and steel samples, respectively. Finally, the corrosion mechanism of the titanium dioxide coatings was characterized and described.

The study discusses the issues of low durability of dies used in the first operation of producing a valve type forging from high nickel steel assigned for the application in motor truck engines. The analyzed process of manufacturing the exhaust valve forgings is realized in the coextrusion technology, followed by forging in closed dies. This process is difficult to master, mainly due to elevated adhesion of the charge material (high nickel steel – NCF3015) to the tool substrate as well as very high abrasive wear of the tool, most probably caused by the dissolution of hard carbide precipitates during the charge heating. A big temperature scatter of the charge during the heating and its short presence in the inductor prevents microstructure homogenization of the bearing roller and dissolution of hard precipitates. In effect, this causes an increase of the forging force and the pressures in the contact, which, in extreme cases, is the cause of the blocking of the forging already at the beginning of the process. In order to analyze this issue, complex investigations were conducted, which included: numerical modelling, dilatometric tests and hardness measurements. The microstructure examinations after the heating process pointed to lack of structure repeatability; the dilatometric tests determined the phase transformations, and the FEM results enabled an analysis of the process for different charge hardness values. On the basis of the conducted analyzes, it was found that the batch material heating process was not repeatable, because the collected samples showed a different amount of dissolved carbides in the microstructure, which translated into different hardnesses (from over 300 HV to 192 HV). Also, the results of numerical modeling showed that lower charge temperature translates into greater forces (by about 100 kN) and normal stresses (1000 MPa for the nominal process and 1500 MPa for a harder charge) and equivalent stresses in the tools (respectively: 1300 MPa and over 1800 MPa), as well as abrasive wear (3000 MPa mm; 4500 MPa mm). The obtained results determined the directions of further studies aiming at improvement of the production process and thus increase of tool durability.