Electrogalvanized Steel Sheets Research Articles

連続スポット溶接時における電極損耗過程に関する検討 Ｚｎ‐Ｎｉ電気めっき鋼板ならびに有機複合被覆鋼板のスポット溶接性 第１報

Electrode life is of significant concern in spot weldability of coated steel sheets. The factors which dominate electrode life are still indistinct, although there has been an extensive number of investigations. One of the reason for this may be that electrode wearing process is not clarified. The purpose of this study is to define the electrode wear process and its mechanism focused on a distinction of alloying layers at electrode face during consecutive welding.Electrode life when consecutive spot-welding Zn-Ni electrogalvanized steel sheet is achieved over 10000 welds, whereas it is only 4000 welds for organic-silicate composite steel sheet. Electrode used on organic-silicate composite steel sheet exhibited more rapid wear than electrode used on Zn-Ni electrogalvanized steel sheet.In the case when welding Zn-Ni electrogalvanized steel sheet, the primary factor in electrode wear is a series of Cu (electrode material)/Zn (coating element) interaction, γCu-Zn formation on electrode face and its peeling off. Zn-Fe alloy is deposited and formed into a projection at the center of electrode face. This projection have a potential for keeping high current density when electrode wear is proceeding. This phenomenon can be thought of as one of the main factors responsible for good consecutive spot weldability.In the case when welding organic-silicate composite steel sheet, electrode/steel interface experiences high temperature exceeding the melting point of Cu-Zn during welding. Therefore, the principal factor of electrode wear would be a series of Cu/Zn interaction, alloying and melting. The locomotion of partial current-passed area is observed during consecutive welding. It would correspond to the movement of micro projection caused by partial current flow and melting on electrode face.

電気亜鉛めっき鋼板の後処理の開発動向

電気亜鉛めっき鋼板の後処理の開発動向

Study of electrode wear mechanism in consecutive spot welding: Spot weldability of Zn-Ni electrogalvanised steel sheet and organic-silicate composite steel sheet (1st Report)

Study of electrode wear mechanism in consecutive spot welding: Spot weldability of Zn-Ni electrogalvanised steel sheet and organic-silicate composite steel sheet (1st Report)

溶融亜鉛めっき鋼板の電極寿命に及ぼすめっき皮膜中のＡｌの影響

The purpose of this study is to investigate the effect of Aluminum in Zn coating on electrode life of galvanized steel sheet. Three hot-dip galvanized and one electro-galvanized steel sheets were prepared for this study. Aluminum content in coatings was changed from 0.26 to 0.87 mass% among three hot-dip galvanized steel sheets.The approach used here included EDX, AES analysis of the coating layers, electrode life tests and EPMA analysis of electrodes after 900 welded.The obtained results are as follows:(1) Electrode lives of HDG materials were changed between less and more than 0.3-0.4 mass% Al content in Zn coating. Materials with low-Al coating content showed over three times longer electrode lives than materials with high-Al coating content.(2) Although thickness of Al oxide layers was in proportion to Al content in Zn coatings, the obvious correlation between electrode life and thickness of Al oxide layers was not observed.(3) In case of low-Al coating content, it was observed that Fe-Zn alloy grew from the steel-coating interface to Zn coating. It was considered that, in the initial stage of welding, the content of Fe in Zn coating increased immediately.(4) In case of high-Al coating content, Fe-Al Alloy was observed at coating-steel interface instead of Fe-Zn alloy. It was known that Fe-Al alloy suppresses Fe-Zn alloying reaction. Zn coatings was not alloyed with Fe on initial stage of welding.(5) From these results, it was concluded that Aluminum in coatings affected electrode life by changing the melting point of coating layers between electrode and steel. Melting point of low-Al content coating layer rose because of the diffusion of Fe into Zn coating. This phenomenon decreased electrode wearing and electrode life was long. In contrast, melting point of high-Al content coating layers remained low. This phenomenon caused electrode alloying easily and also increase electrode wearing. As the result, electrode life became shorter.

A phenomenological model for frictional contact of coated steel sheets

A simple phenomenological model for frictional contact with hardening is proposed. The objective is to simulate the frictional behaviour of coated steel sheets subjected to large sliding distances. Within the context of thermodynamics with internal variables, the friction coefficient is assumed to be a function of the frictional work resulting in a theory analogous to classical work-hardening elastoplasticity. The technique for experimental identification of the proposed model is described briefly and the material parameters obtained for Electrogalvanised steel sheet and BAF Al-killed steel sheet are presented. Within the computational scheme, a robust algorithm based on an operator split method (elastic predictor-frictional sliding corrector) is used for numerical integration of the friction constitutive equations. The finite-element simulation of a series of sliding tests is carried out and the results are compared with experiments.

Development of a new organic composite coated steel sheet with high corrosion resistance

To meet the recent requirement of high quality and performance of pure zinc electrogalvanized steel sheet, a study on a new organic composite coated steel sheet, called anti-fingerprinted steel sheet, has been carried out. The substrate was pure zinc electrogalvanized sheet with a metallic coating of 20 g m -2. Two different processes for inorganic (chromating) and organic (resin) coating were applied. One was a two coat/two bake type consisting of separate chromating and resin coating treatments which is now widely used. The other, newly developed for this study, was a one coat/one bake type with simultaneous treatments. The solution used for the one coat/one bake type was an water-based coating agent which was composed of both inorganic and organic components. The new organic composite coated sheet possesses superior corrosion resistance, and good paintability, formability and fingerprint resistance properties.

Influence of plastic strain on friction in sheet metal forming

A sheet metal forming simulator which stretches a strip around a cylindrical pin was used to investigate the relationship between friction and process variables including sliding speed, strip strain and strain-rate in the boundary lubrication regime. Measurements were conducted with two different sheet and tooling material combinations: electro-galvanized steel sheet on smooth A2 tool steel and commercially pure aluminum sheet on cemented carbide. In the first system, friction tends to increase with strain in contact. This supports a friction model which treats the influence of plastic strain on the flattening of strip asperities and real area of contact. In the second system friction was found to decrease with the strain in contact. This is apparently due to a decrease in contact area associated with roughening of the strip by plastic deformation.

クロメート処理亜鉛めっき鋼板の性能と皮膜構造に及ぼすりん酸およびコロイダルシリカの添加効果

クロメート処理亜鉛めっき鋼板の性能と皮膜構造に及ぼすりん酸およびコロイダルシリカの添加効果

MODIFICATION OF THE COMPOSITION OF LASER WELDS IN ELECTROGALVANIZED STEEL AND THE EFFECT ON CORROSION PROPERTIES

Abstract Compositional modification of the weld metal during laser welding of electrogalvanized steel sheet was achieved by the injection of metal powder or by a technique in which zinc that had been volatilized as a result of the welding operation was redeposited on the weld bead. Corrosion testing by means of the linear polarization technique showed that the coating corrosion rate in the case of laser welds containing redeposited zinc was substantially lower for an initial period than for normal laser welds. Only a small decrease in corrosion rate was achieved by the injection of tool steel powder during laser welding while an increase in coating corrosion rate was produced by the injection of nickel powder or stainless steel powder

Modifications of the phosphate coatings microcrystalline structures induced by dehydration and rehydration processes

Bare and electrogalvanized steel sheets were subjected to phosphatation in three different phosphatation baths. The aim of the work was to characterize and to compare the behaviour of pure hopeite, phosphophyllite and manganese modified hopeite crystals during dehydration and rehydration processes. Scanning electron microscopy, thermal analysis and X-ray diffractometry were employed to study the obtained phosphate coatings. Thermogravimetric analysis showed that all the considered phases underwent the total loss of two water molecules above 150° C. X-ray diffraction measurements showed the formation of bihydrated phases which appear very similar independently from the use of the phosphatation bath. After exposure to a hydrating environment only the pure hopeite bihydrated crystals underwent a rehydration process which led to the tetrahydrated phase and consequently to a decreased paint-phosphate adhesiveness. On the contrary both the bihydrated phosphophyllite phase and the bihydrated manganese modified hopeite phase revealed their inability to return to the completely hydrated crystal and consequently improved paint adhesion.

Effects of heavy metal additions and crystal modification on the zinc phosphating of electrogalvanized steel sheet

The action of the heavy metal components in zinz phosphating solution was investigated for the electrogalvanized side and the steel side of zinc-coated steel sheet. Ni 2+ and Mn 2+ in the solution enter into the hopeite crystal that forms on the electrogalvanized side and modify the crystals. The crystal size is refined according to increase in the nickel-plus-manganese content, and there is a corresponding increase in the adhesiveness of the paint film. The paint film adhesiveness on hopeite that contains more that 5 wt.% Ni + Mn in the crystal becomes equivalent to that on phosphophyllite. From these results and differential thermal analysis data, it is concluded that the chemical structure of hopeite becomes similar to that of phosphophyllite by the crystal modification.

電気亜鉛めつき鋼板の加熱による合金化挙動

電気亜鉛めつき鋼板の加熱による合金化挙動

電気亜鉛めっき鋼板の表面特性に及ぼす金属添加の影響

電気亜鉛めっき鋼板の表面特性に及ぼす金属添加の影響

電気亜鉛めっき鋼板の耐食性に及ぼす浴中の金属イオンの影響

The effects of metal ions in plating bath such as Fe, Co, Ni, Cr, Mo, W, Mn, Cu, or Sn on the properties of electrogalvanized steel sheet were investigated by corrosion resistance and paint adhesion tests. The results are summarized as follows: (1) The range of adequate current density is broader in the bath containing Fe, Co, Ni or W ions, and narrower in the bath containing Cr, Sn or Cu ions. (2) The surface appearance of plated sheet is greatly affected by the sort and quantity of metal ion in the plating bath. Plated sheet has a tendency to show fine structure, as metal ions of Fe, Co or Ni in the bath increases. In the case of containing Mo or Cr ions in the bath, it shows massive structure. (3) The effect of additive element on the corrosion resistance of plated sheet is greatly affected by the corrosion circumstances. In salt spray test, for example, plated sheet obtained from the bath containing Sn or Cr ions has more excellent corrosion resistance than the conventional zinc plated sheet. On the other hand, in the outdoor exposure test and humidity test, it has less excellent corrosion resistance. Plated sheet obtained from the bath containing Co or Ni ions has more excellent corrosion resistance than the conventional zinc plated sheet in any test. (4) Plated sheet obtained from the bath containing Co, Mo, Cr, W or Fe ions has always more excellent corrosion resistance or more excellent paint adhesion after corrosion test than the conventional zinc plated sheet, though it is greatly affected by the sorts of paints and corrosion circumstances. Among these metal ions, Co ion has the greatest effect on the corrosion resistance.

Manufacturing of one-side electrogalvanized steel strip with heavy coating.

In the electrogalvanizing, one-side galvanizing method is said to be rather easy from the view point of its principle, but in practice, the various plating equipment currently in service require special arrangements.The manufacturing process developed for one-side electrogalvanized steel strip with heavy coating based on the horizontal cell system is described.Throw-around of zinc deposit on the uncoated surface can be minimized by reducing the depth of the electrolyte above the strip.Edge overcoating is prevented with the use of edge masks. A high current density operation was made possible by increasing electrolyte flow rate between the strip and the anode.With these measures, one-side electrogalvanized steel sheets with clean zinc surface without burnt deposit, free from stains on the uncoated surface are being manufactured.

電気亜鉛めっき鋼板の亜鉛拡散に及ぼす共析鉛の影響

The effect of co-deposited lead on the property of electrogalvanized steel sheets after heat treatment was studied, especially from the viewpoint of adherence of the zinc layer. In the process of alloy formation between the deposited zinc and steel sheets by heat treatment, the co-deposited lead atoms concentrate at the interface between the zeta-phase layer and the zinc layer, and thus restrain the formation of the alloy layer. The peel-off phenomenon of the zinc layer were found when the quantity of the alloy layer exceeds a certain limit which is defined as ξ al. This value decreases with an increase in the lead concentration of the deposit. It is supposed that the lead atoms concentrated at the interface accelerate the formation of cavities as a result of the gathering of vacancies, and that, the peel-off of the zinc layer is due to the accelerated Kirkendall effect.