This study presents arc surface remelting of three types of sintered stainless steels carried out in order to constitute a homogeneous microstructure in the surface layer which is free from open and interconnected porosity. The main aim of this treatment was to improve functional properties of the sinters analysed, especially their resistance to pitting corrosion. The sinters were obtained from powders of 316 L and 434 L steels. The PM austenitic-ferritic stainless steels are used mainly in the automotive industry, but their general application is still limited due to relatively poor corrosion properties when compared to casts or wrought components. This study used the gas tungsten arc welding (GTAW) process as a method of economical surface treatment. The effect of surface treatment was evaluated based on macro-and microstructural observations, energy-dispersive X-ray spectroscopy (EDX) analysis, X-ray phase analysis, measurements of surface roughness and electrochemical examinations. It was found that a cellular or mixed cellular and dendritic structure was formed in the remelted zone of the sinters after remelting. X-ray analysis demonstrated that application of remelting contributes to formation of the austenitic phase in the surface layer. The corrosion resistance of the remelted surface layers was evaluated using polarization tests in 0.5 M NaCl solution. It was found that arc surface remelted layers exhibit much better anticorrosive properties than sinters without surface treatment. Microstructural observations of the surface of specimens after electrochemical tests showed only a few single pits in the remelted layer, while the surface of initial sinters was much more corroded.

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WPŁYW pH ROZTWORU NA SZYBKOŚĆ KOROZJI SPIEKANYCH STALI NIERDZEWNYCH STOSOWANYCH NA OKŁADKI OGNIW PALIWOWYCH Z MEMBRANĄ POLIMEROWĄProton exchange membrane fuel cells (PEMFCs) are numbered among low-temperature cells. Their operating temperature reaches 120• C, whereas their efficiency amounts to ca. 40%. These cells are most often used for the batteries for portable devices, low and high power generators, stationary power plants and car drives. The PEMFCs are composed of the membrane, electrodes at both sides and bipolar plates, also termed interconnectors.The main aim of the present study was to investigate the sintered stainless steels in simulated environments of a PEM fuel cells for bipolar plates. The ferritic (434L) and austenitic (316L) stainless steels were examined. The corrosion properties were examined in 0.1 mol dm −3 Na 2 SO 4 + 2 ppmF − (pH= 1; 3; 5) at 80 • C. Keywords: fuel cell, bipolar plates, corrosion, sintered stainless steel, structural analysis, corrosion resistance Ogniwa paliwowe z membraną protonowymienną są jednym, z niskotemperaturowych ogniw. Ich temperatura pracy wynosi 120• C, a sprawność dochodzi do 40%. Tego typu ogniwa są najczęściej używane jako generatory do urządzeń przenośnych, małych i średnich stacjonarnych elektrowni i do napędu samochodowego. Ogniwa PEMFC (Proton Exchange Membrane Fuel Cell) składają się z membrany, elektrod po obu jej stronach oraz okładek, nazywanych też interkonektorami. Głównym celem niniejszej pracy było zbadanie spiekanych stali nierdzewnych przeznaczonych na okładki, w symulowanych środowiskach ogniw paliwowych PEMFC. Badano stal ferrytyczną (434L) oraz austenityczną (316L). Odporność korozyjna stali badano w 0.1 mol dm −3 Na 2 SO 4 +2 ppmF − (pH= 1; 3; 5) w temperaturze 80• C.

The Friction stir welding (FSW) is a complex process, depending on many factors: machine, clamping device, material and tools. Parameters that have a direct impact on the quality of the joint include the rotational speed, welding speed, clamping force, geometry and tool plunging depth. The paper presents the results of experimental studies concerning the effect of tool pin length on the microstructure and mechanical strength of joints of thin sheets made of Al 7075 alloy. A tool with an adjustable pin with concave shoulder was used to weld the joints. Different pin lengths were used, which were selected with respect to the thickness of the welded joint. The specimens were subjected to visual evaluation, metallographic tests and mechanical strength testing. The results indicate that the pin length has a decisive effect on the microstructural changes in the joint and thus influencing the strength of the FSW joints.

The aim of this paper was to present preliminary results of researches conducted in PZL Mielec within the FAST_FSW project (INNOLOT program) on the influence of tool eccentricity on microstructure and mechanical properties of 1.6 mm and 0.8 mm thick Al 7075 T6 sheets joints. Samples were performed using CNC milling machine. The range of tool eccentricity was 0-0.3 mm, rotational speed and feed rate were variable. The influence of the applied welding parameters on microstructure and mechanical properties of joints was assessed on the basis of metallographic inspections and tensile tests. Microstructural observations have shown that the change of FSW tool eccentricity affects the weld geometry: the mixing zone depth, the weld width, or the shape of the contact line.

Aluminum structures, and in particular an element of aerostructures, are strongly exposed to the effects of weather conditions. In the case of using new techniques of joining these structural elements, the selection of proper corrosion protection without losing the required properties of the joint may determine its potential application. This paper presents the results of experimental research concerning the influence of corrosion protection on the microstructure and mechanical strength of resistance spot welded (RSW) and refill friction stir spot welded (RFSSW) joints. The tests were carried out on 2024 T3 aluminum alloy, both sides alcladed. For comparison purposes, the following joints were welded: without any protection, with the primer layer, with anodic oxide coating, and with anodic oxide coating plus sealant between the overlapping surface of the welded metal sheet. The samples were visually inspected, and metallographic and mechanical strength examination was conducted. The test results indicate that the application of the protective layers and its type have an impact on the strength of RSW and RFSSW joints. The use of an adhesive or sealant in welded joints provides an increase in the load capacity of the joint.

This study presents the results of the investigations of the effect of surface remelting using arc welding (GTAW) on the microstructure and selected properties of surface layer of sintered steels 304L and 434L. It was found that in order to improve surface quality in these sinters, remelting should be carried out at lower current intensities, i.e. 30A and 40A. The surface treatment carried out in the study allowed for obtaining an uniform cellular-dendritic microstructure in surface layer. X-ray examinations demonstrated the effect of compressive stress in surface layer, which reduces the risk of cracking on the surface.

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