The paper deals with evaluation the corrosion characteristics of welded joints in two corrosion environments – SARS and 0.1 M NaCl solution. Welds were made by MAG technology using three protective gas mixtures - Ferroline He20C8, Ferroline C18 and Ferroline C6X1. There were realised chemical analysis of the base material and weld metal of all welded joints, Vickers hardness test of the base material, heat affected zones and weld metals, metallographic analysis of all areas of welds and measurement of base and weld metal corrosion rate in two corrosion environments. Hardness increases from the base material through the HAZ to the weld metal. The maximum difference between the hardness of the weld metal and the base material is 36 HV 0.1 - realised welds do not show a notch effect. The corrosion rate of the materials in SARS solution was higher than in the NaCl solution. The corrosion rate in weld metals of all welded joints was lower than the corrosion rate of the base material. The lowest corrosion rate in both corrosive environments showed a weld metal made using shielding gas Ferroline C18.
Acrylate varnishes are due to their suitable properties frequently used in restoration and preservation on variety of historical objects and materials. Common practice of their application involves using as an adhesive agents, consolidants and protective coatings. The purpose of protective coatings especially on metal artefacts is to reduce access of pollutants to the surface of the artefact. In this paper, coatings prepared from two acrylate polymers Paraloid B72 and Paraloid B48N are compared in terms of permeability for water and level of protective properties against air pollutants. For this purpose, electrochemical impedance spectroscopy and resistometric method were chosen for analysis of the coatings. Obtained results show lower permeability for water in case of Paraloid B72. However, same coating provided lower protection against air pollutants than Paraloid B48N coating.
Increasing the functional parameters of coating composition-based protective coatings is a strongly emerging trend. However, there are some limits to the increasing of utility parameters of protective coatings – always where such parameters are opposite to the basic property, which is corrosion protection. The presented study describes a case of a premature failure in the corrosion protection secured by a duplex system that occurred after the paint system had been enriched with an anti-sliding property.
Nowadays, number of customer and environmental requirements are laid to the automotive industry. These are related to safety increase, the weight and emission reduction as well as the life-time improvement. The article presents the way to improve the corrosion resistance of the car-body components when coated steel sheets are used based on Zn-Al-Mg coatings. Thus, the life-time of the car-body is improved. Samples with conventional Zn coating and samples with advanced Zn-Al-Mg coatings were deformed by stretching and 3-point bending to 90° and 180° tests. Consequently, the samples were exposed to salt spray in the corrosion chamber. Time to red corrosion appearance and adequate percentage of corroded surface was evaluated. The results showed the better corrosion protection of Zn-Al-Mg coatings when compared to the conventional Zn coating.
J. Tkacz, K. Slouková, J. Minda, J. Drábiková, S. Fintová, P. Doležal and J. Wasserbauer
Corrosion behavior of wrought magnesium alloys AZ31 and AZ61 was studied in Hank’s solution. Potentiodynamic curves measured after short-term of exposure showed higher corrosion resistance of AZ31 magnesium alloy in comparison with AZ61 magnesium alloy. On the contrary, long-term tests measured by electrochemical impedance spectroscopy showed higher corrosion resistance of AZ61 magnesium alloy in comparison with AZ31 magnesium alloy.
The article is aimed at evaluation of chosen properties of thermally sprayed coatings based on tungsten carbide. It was evaluated two types of coatings – WC-FeCrAl and WC-WB-Co. The coatings were deposited on basic material steel AISI 316L. The aim of experimental works was to determine the quality and resistance of coatings in corrosion environment depending on number of thermal cycles. The quality of coatings was evaluated by determination of their adhesion depending on thermal cycles, determination of microhardness and indentation fracture toughness. Coatings were exposed in tribo-corrosion conditions with the presence of 1% NaCl. The results of experimental showed a higher quality of coating WC-WB-Co.
This paper presents the results of research aimed to measuring the corrosion properties of EDDQ steel sheet. The strain amount influence to the corrosion properties of the steel sheet for drawn parts has been proven by the modern methods of corrosion monitoring such as Electrochemical Impedance Spectroscopy. Corrosion rate was assessed using electrochemical methods in 0.1 M solution of NaCl. Experimental studies have pointed out if strain amount increases the corrosion rate of the steel sheet increases too.
F. Pastorek, K. Borko, S. Dundeková, S. Fintová and B. Hadzima
Large number of mechanical and chemical surface pretreatment techniques is actually used on steels in industrial practice. Choosing the right combination of these technologies is one of the most important tasks for many applications. The purpose of this research was to evaluate the influence of selected mechanical surface preparation methods (grinding, sandblasting) on the quality and electrochemical corrosion characteristics of S355J2 steel before and after the final chemical surface treatment by the technology of manganese phosphating. The surface morphology of the formed phosphate layer was evaluated by a scanning electron microscopy (SEM) and the cross section analysis was performed by a light metallographic microscopy. 0.1M Na2SO4 solution simulating aggressive industrial pollution was selected for electrochemical corrosion tests. Impact evaluation of various mechanical and chemical surface treatments on the corrosion properties of the tested steel was realized by potentiodynamic polarization tests (PD) and electrochemical impedance spectroscopy (EIS) using the Tafel analysis and equivalent circuits method respectively. The obtained results proved that sandblasting negatively affected the corrosion resistance of S355J2 steel and subsequently created manganese phosphate layer.
This paper is focused on the heteropoly acids as another new possibility of dopant for conducting polymers which can be used as anticorrosive pigments for steel protection. The newly prepared pigments, silicotungstic and phosphotungstic heteropoly acids, were characterized by determination of oil number and density. The value of critical pigment volume concentration was determinated by these values. The pigment volume concentration was 0.5; 1; 3 and 5 % in epoxyester-resin witch was used as a binder. Organic coatings were applicated on steel panels which were tested by mechanical and corrosion tests. The main exam was exposition of testing sample in sulphur dioxide atmosphere. Another important exam was measuring the specific electrical conductivity and determination of corrosion loss. After 1584 hours, the samples were evaluated. Values of anticorrosion efficiency are increased for silicotungstic heteropoly acid pigment. But with long-term exposition, phosphotungstic heteropoly acid pigment has better and higher anticorrosion efficiency than the other sample.
J. Drábiková, F. Pastorek, S. Fintová, P. Doležal and J. Wasserbauer
Magnesium and its alloys are perspective bio-degradable materials used mainly due to their mechanical properties similar to those of mammal bones. Potential problems in utilization of magnesium alloys as bio-materials may relate to their rapid degradation which is associated with resorption problems and intensive hydrogen evolution. These problems can be eliminated by magnesium alloys surface treatment. Therefore, this work aims with analysis of the influence of fluoride conversion coating on corrosion characteristics of magnesium alloy. Unconventional technique by insertion of wrought magnesium alloy AZ61 into molten Na[BF4] salt at temperature of 450 °C at different treatment times was used for fluoride conversion coating preparation. The consequent effect of the coating on magnesium alloy corrosion was analyzed by means of linear polarization in simulated body fluid solution at 37 ± 2 °C. The obtained results prove that this method radically improve corrosion resistance of wrought AZ61magnesium alloy even in the case of short time of coating preparation.