ELECTRICAL CONTACT APPLICATION OF A ZINC COATING ON A THREADED PART OF A FUDAMENT BOLT

Proposals for a more rational application of zinc coating on the threaded part of the base bolt.

Gas brazing of thin-sheet galvanized steel with aluminum solders

. In this work, the first stage of experimental research was carried out to estimate the main physicochemical processes that determine the qualitative characteristics of a brazed joint made of thin sheet galvanized steel during gas brazing with aluminum solder systems. In particular, an estimation was made of the ability of spreading and wetting of aluminum solders (AlSi5, AlSi12) on the surface of thin sheet galvanized steel ( DX56D + Z of 0.4 mm thick and zinc-coated layer of 45–65 microns) at a step-by-step increase in the heating area of the base metal in the presence and absence of flux (Al-Flux 726). The aluminum alloys was heated “not directly,” but through the base metal to maximize the preservation of the anticorrosive zinc coating at the interface between the liquid solder and the base material.

Modeling of physical wear assessment of zinc coating of space steel frame road structures for road safety information systems

The article developed an improved physical and mathematical model of the corrosive wear of zinc coating of steel structures in a city. The research is based on full-scale experimental data for determining the wear of a zinc coating of full-scale metal spatial structures of frame road structures for informational safety systems on roads after 10 years of operation in the conditions of Kyiv. The frame structure consists of metal columns and a steel crossbar frame. The crossbar frame is a spatial block of two steel trusses. The block of trusses is assembled from unified spatial sections united by vertical and horizontal ties, and which are connected by flange nodes of a special design. All structural elements are made of rolled tubes. Based on the research results, an approach to assessing the physical wear of the zinc coating of the spatial structural system is proposed. According to the peculiarities of the arrangement of elements in frame structures, and, accordingly, to different conditions and operations, an approach is proposed to assess the corrosive wear of a zinc coating for various groups of elements: columns, spatial block of two steel trusses, flange nodes. The physical and mathematical model is based on the working hypothesis of uneven wear of the zinc coating over time. It was found that for each group of structural elements, the conditions of the gaseous environment, the effects of atmospheric precipitation, wind speed, temperature changes individually affect the reduction of the zinc coating. The obtained experimental data were used to determine the parameter of the rate of decrease in the zinc coating of the physical and mathematical model. The results of the research and the development of the methodology helped to establish the operating conditions of the zinc coating according to the criterion of the rate of wear of the zinc coating, to classify the category of aggressiveness of the environment for each group of structural elements. Also, studies allow predicting the service life by reducing the thickness of the zinc coating, as well as the wear of the zinc coating in time in the subsequent period of operation. The methodology is universal and can be extended to other types of galvanized metal structures.

Effect of Zinc Coating on Delay Nugget Formation in Dissimilar DP600 - AISI304 Welded Joints Obtained by the Resistance Spot Welding Process

This paper researches the effect of zinc coating of galvanized DP600 steel on the dynamic resistance and the delayed nugget formation of dissimilar DP600 - AISI304 welded joints, obtained with resistance spot welding process (RSW). The RSW evaluations consisted of determining, from the dynamic resistance curves, the time involved in the different stages of the process, particularly the beginning of nugget formation. The experimental results showed that, from the dynamic resistance curves, it is possible to identify 8 distinct stages during the welding of galvanized DP600 steel and AISI304 stainless steel. In the case of the welding of uncoated DP600 steel with AISI304, only 6 stages are identified (except for stages 2 and 3), which are directly related to the heating, softening and melting of the galvanic coating. The energy used in stages 2 and 3, causes a delay in the beginning of nugget formation for welded joints obtained with galvanized DP600 steel compared to uncoated DP600 - AISI304 welded joints, reaching values between 37.28 ms and 52.29 ms for the welding conditions analyzed. Monitoring the time duration of stages 2 and 3, as defined from the analysis of the dynamic resistance curves, could be used as a tool to predict the beginning of nugget formation in the welding of galvanized steels, to avoid undesirable phenomena such as expulsion and to guarantee the quality of the welded joints.

Effect of Rare Earth Element La on Corrosion Resistance of Powder Zinc Coating: Experiment and First Principle Calculation

Using a combination of first-principles calculations and experimental studies to study the effect of La on the corrosion resistance of Powder sherardizing layer in metal structures. Compared to other sherardizing rare earth elements (Re), La has better adsorption with the iron matrix and has the lowest binding energy on the adsorption surface (111) of the Fe matrix. Therefore, the rare earth element La is added to the powder sherardizing process for the rare earth chemical heat treatment to reduce the defects of the powder sherardizing faults formed, improve the surface uniformity and the quality of the permeation layer. On the basis of calculation, La element was added in the process of powder sherardizing, and the corrosion performance of the formed powder galvanizing layer was studied. After alternating salt spray experiments, the degree of corrosion of the layer is relatively small and the corrosion products are predominantly layered and spherical. Electrochemical tests of the layer show that the corrosion resistance of the layer after the rare earth chemical heat treatment has improved.

Laser-TIG welding of galvanized steel – numerical and experimental assessment of the effect of arc in various setups

The technology of laser-TIG welding utilizes the arc as a secondary heat source during laser welding. In TIG-leading configuration, the low-current arc precedes the beam to preheat the material. The numerical simulations representing various setups combining laser and arc were performed to study the changes of thermal cycles on the interface of thin metal sheets of overlap joint. The relations between the position of the arc towards the beam, additional heat input, and temperature gradients are discussed. The technology of laser-TIG welding of zinc-coated deep-drawing steel was experimentally applied in the same joint configuration. A good agreement between the calculated and experimental welds was achieved. The arc current less than 40 A did not cause the vaporization, neither oxidation of zinc coating on the interface surface of metal sheets. Nevertheless, the quality of laser-TIG welds was better compared to laser welds. The 40A arc current increased the heat input by about 50% and led to an almost 60% decrease in cooling rate compared to autonomous laser welding. Prolonged heating and cooling time are the key factors of improving the weld quality.