CN101748396A - Preparation method of magnesium alloy rare-earth conversion coatings for ethylene glycol cooling system - Google Patents
Preparation method of magnesium alloy rare-earth conversion coatings for ethylene glycol cooling system Download PDFInfo
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Abstract
The invention discloses a preparation method of magnesium alloy rare-earth conversion coatings for an ethylene glycol cooling system, which includes a process of pretreatment and activating and chemical conversion coating. The prepared rare-earth conversion coating has even thickness and good surface consistence, has good corrosion-resistant performance in ethylene glycol-water cooling liquid, and can solve the problem of the severe corrosion of engine cooling system used magnesium alloy in cooling liquid.
Description
Technical field
The invention belongs to magnesium alloy surface treatment, be specifically related to the preparation method of a kind of ethylene glycol cooling system with the magnesium alloy surface rare earth conversion film.
Background technology
The automobile lightweight is to reduce oil consumption and reduce one of effective measure of discharging, and magnesium alloy is acknowledged as the most promising now automobile lightweight material.In automobile cooling system, adopt magnesium alloy to have good loss of weight potentiality and application prospect, but must be in the face of the etching problem of cooling fluid to magnesium alloy.Cooling fluid is the indispensable heat-transfer medium in the engine-cooling system, and present commercial cooling fluid all is ethylene glycol-aqueous systems basically.Different materials of using always in the engine system such as steel, aluminium alloy, copper etc. all can satisfy corresponding life standard substantially in the general commercial cooling fluid.
Yet the standard potential of magnesium alloy is low, chemistry and electrochemical activity height, and the non-constant of corrosion resistance nature in cooling fluid has become its important bottleneck of using of restriction in cooling system.For example, the magnesium alloy engine that external motor corporation makes, do not carry out the test and the protection of the corrosive nature of magnesium alloy in cooling fluid, directly magnesium alloy engine is carried out dynamics simulation, the several months test-results shows, the magnesium alloy cooling system by heavy corrosion [Song Guangling. the magnesium alloy corrosion and protection. Beijing: Chemical Industry Press, 2006].To studies show that of magnesium alloy corrosion inhibitor in the cooling fluid [Liu Yuangang. the research of magnesium alloy corrosion inhibitor in the automobile engine cooling liquid. corrosion science and guard technology, 2005,17 (2): 8], magnesium alloy is had a positive effect in cooling fluid special inhibiter can produce serious corrosion to other metals in the system to a great extent.Therefore it being carried out surface treatment is to prevent that magnesium alloy from corroding valid approach in cooling system.
Because the engine cylinder-body cooling system is mainly the circulating cooling pipe road, shape that it is special and environmental restraint the application of process for treating surface such as differential arc oxidation, vapour deposition, laser treatment, spray treatment, and the chemical conversion membrane processing method can overcome above technical deficiency.What have magnesium alloy conversion film technical maturity now is chromate conversion coating, phosphoric acid salt and rare-earth conversion coatings etc.Patent publication No. is the chromate conversion coating excellent performance of CN1880503A preparation, but environmental pollution is serious.Publication number is that the phosphoric acid salt composite membrane rete of CN1236104C preparation is not fine and close, need make sealing of hole and handle, and the formula solution complicated component.Yet, also seldom disclose at present and be applicable to the surface rare earth conversion film treatment process of engine-cooling system with magnesium alloy.
Summary of the invention
The object of the present invention is to provide a kind of preparation method of Mg alloy surface environment-friendly type rare-earth conversion coatings, the conversion film even film layer densification of preparation, in ethylene glycol-water coolant system, have excellent corrosion resistance nature, can solve the problem of engine-cooling system with magnesium alloy heavy corrosion in cooling fluid.
The objective of the invention is to be achieved through the following technical solutions:
A kind of preparation method of magnesium alloy rare-earth conversion coatings for ethylene glycol cooling system is characterized in that this method may further comprise the steps successively:
A, pre-treatment and activation: adopt mechanical grinding and washing composition to remove to clean Mg alloy surface oxide film and dirt, put into acetic acid with distilled water flushing after clean then or oxalic acid solution carries out activation treatment.
B, chemical conversion membrane prepare: it is the ammonium borate of 15～25g/L and the cerous sulfate composite solution of 10～20g/L that the magnesium alloy after will activating places concentration, temperature is controlled to be 80～100 ℃, treatment time is 15～20 minutes, taking out then and putting into concentration is that the ammonium fluoride solution of 3.5～5wt% soaked 15～20 minutes, can generate one deck white rare-earth conversion coatings at Mg alloy surface after taking out cleaning, drying.
Magnesium alloy rare-earth conversion coatings thicknesses of layers by the present invention preparation is at 3～4 μ m.
The method of evaluating performance of the rare-earth conversion coatings of the present invention's preparation is as follows:
Surface topography and composition: with the surface microscopic topographic of JSM-5600LV type scanning electronic microscope and JSM-6701F awkward silence at a meeting emission type scanning electron microscopic observation conversion film, test result: the conversion film surface combines closely with magnesium alloy substrate, rete is evenly fine and close, and the conversion film grain diameter is at 60～150nm.Adopt the crystalline structure and the composition of X-ray diffractometer and x-ray photoelectron spectroscopy test rare-earth conversion coatings; rete is mainly the oxide compound of cerium and the oxide compound and the oxyhydroxide thereof of magnesium, and the complex oxide film that these particles are tiny provides better corrosion protection for magnesium alloy.
Corrosion resistance nature: utilize the method for electrokinetic potential polarization test to estimate its corrosion resisting property, employing standard three-electrode system, sample are working electrode, and platinum filament is a supporting electrode, saturated calomel electrode is a reference electrode, tests in concentration is ethylene glycol-water simulated engine cooling fluid of 70Vol.%.The result compares with pure magnesium alloy, and the rare-earth conversion coatings corrosion potential of prepared of the present invention has improved 400～600mV, and corrosion electric current density has reduced nearly 2 orders of magnitude.
Employing the present invention have the following advantages:
1, preparation conversion coating treating fluid composition is simple, and does not contain hexavalent chromium compound used in the traditional chemical conversion process, is the rare-earth conversion coatings of chromium-free environment-friendly.
2, rare-earth conversion coatings thickness evenly, surface compact is good, good with matrix bond, has excellent corrosion resistance nature in ethylene glycol-water coolant, can solve the problem of engine-cooling system with magnesium alloy heavy corrosion in cooling fluid.
Embodiment
Embodiment 1
Handling sample is die casting AZ91D magnesium alloy, and size is respectively the sheet flat work pieces of 100mm * 100mm * 2mm, and its concrete operations step is:
1, sample pretreatment and activation: the mechanical grinding sample surfaces is to its roughness R
a≈ 0.18 μ m adopts common washing composition that the back sample surfaces of polishing is cleaned and removes greasy dirt, uses distilled water flushing, puts into concentration then and is 3～5% acetum and activate 1～2 minute.
2, chemical conversion membrane prepare: it is the ammonium borate of 25g/L and the cerous sulfate composite solution of 12g/L that the magnesium alloy after will activating places concentration, temperature is controlled to be 80 ℃, treatment time is 20 minutes, the ammonium fluoride solution of putting into concentration then and be 3.5wt% soaked 20 minutes, after taking out the surperficial one deck black reaction resistates of flushing, can obtain one deck even compact at Mg alloy surface, the white bright rare-earth conversion coatings of color and luster.
Surface microscopic topographic with JSM-5600LV type scanning electronic microscope and JSM-6701F awkward silence at a meeting emission type scanning electron microscopic observation conversion film, test result: the conversion film surface combines closely with magnesium alloy substrate, rete is evenly fine and close, and the conversion film grain diameter is at 60～150nm.Potential polarization test result corrosion potential is the result compare with pure magnesium alloy, and corrosion potential has improved nearly 600mV, and corrosion electric current density has reduced nearly 2 orders of magnitude.
Embodiment 2
Handling sample is die casting AZ91D magnesium alloy, and size is respectively the sheet flat work pieces of 100mm * 100mm * 2mm, and its concrete operations step is:
1, sample pretreatment and activation: the mechanical grinding sample surfaces is to its roughness R
a≈ 0.18 μ m adopts common washing composition that the back sample surfaces of polishing is cleaned and removes greasy dirt, uses distilled water flushing, puts into concentration then and is 3～5% acetum and activate 1～2 minute.
2, chemical conversion membrane prepare: it is the ammonium borate of 15g/L and the cerous sulfate composite solution of 15g/L that the magnesium alloy after will activating places concentration, temperature is controlled to be 100 ℃, treatment time is 30 minutes, the ammonium fluoride solution of putting into concentration then and be 4wt% soaked 15 minutes, after taking out the surperficial one deck black reaction resistates of flushing, can obtain one deck even compact at Mg alloy surface, the white bright rare-earth conversion coatings of color and luster.
With the surface microscopic topographic of JSM-5600LV type scanning electronic microscope and JSM-6701F awkward silence at a meeting emission type scanning electron microscopic observation conversion film, the conversion film surface combines closely with magnesium alloy substrate, and rete is evenly fine and close, and the conversion film grain diameter is at 60～150nm.Potential polarization test result corrosion potential is the result compare with pure magnesium alloy, and corrosion potential has improved about 400mV, and corrosion electric current density has reduced by 1 most magnitude.
Embodiment 3
Handling sample is the tubular workpiece (inner tubal wall processing) that die casting AZ91D magnesium alloy is 2mm for long 400mm diameter, and its concrete operations step is:
1, sample pretreatment and activation: the mechanical grinding sample surfaces is to its roughness R
a≈ 0.18 μ m adopts common washing composition that the back sample surfaces of polishing is cleaned and removes greasy dirt, uses distilled water flushing, puts into concentration then and is 3～5% acetum and activate 1～2 minute.
2, chemical conversion membrane prepare: it is the ammonium borate of 20g/L and the cerous sulfate composite solution of 10g/L that the magnesium alloy after will activating places concentration, temperature is controlled to be 80 ℃, treatment time is 15 minutes, the ammonium fluoride solution of putting into concentration then and be 4wt% soaked 20 minutes, after taking out the surperficial one deck black reaction resistates of flushing, can obtain one deck even compact at Mg alloy surface, the white bright rare-earth conversion coatings of color and luster.
With the surface microscopic topographic of JSM-5600LV type scanning electronic microscope and JSM-6701F awkward silence at a meeting emission type scanning electron microscopic observation conversion film, it is tight that conversion film surface and magnesium alloy substrate combine the school, the rete densification, and the conversion film grain diameter is at 60～150nm.Potential polarization test result corrosion potential is the result compare with pure magnesium alloy, and corrosion potential has improved about 500mV, and corrosion electric current density has reduced by 1 most magnitude.
Claims (1)
1. the preparation method of a magnesium alloy rare-earth conversion coatings for ethylene glycol cooling system is characterized in that this method may further comprise the steps successively:
A, pre-treatment and activation: adopt mechanical grinding and washing composition to remove to clean Mg alloy surface oxide film and dirt, put into acetic acid with distilled water flushing after clean then or oxalic acid solution carries out activation treatment;
B, chemical conversion membrane prepare: it is the ammonium borate of 15～25g/L and the cerous sulfate composite solution of 10～20g/L that the magnesium alloy after will activating places concentration, temperature is controlled to be 80～100 ℃, treatment time is 15～20 minutes, taking out then and putting into concentration is that the ammonium fluoride solution of 3.5～5wt% soaked 15～20 minutes, can generate one deck white rare-earth conversion coatings at Mg alloy surface after taking out cleaning, drying.
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| CN108048831A (en) * | 2017-12-14 | 2018-05-18 | 马鞍山新徽铝业有限公司 | A kind of method that aluminium alloy blacks |
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| FR2825378B1 (en) * | 2001-05-31 | 2003-11-28 | Univ Paris Curie | COMPOSITION AND METHOD FOR THE TREATMENT OF MAGNESIUM ALLOYS |
| CN100595328C (en) * | 2006-09-28 | 2010-03-24 | 比亚迪股份有限公司 | Composition for surface treatment of light metal and its composite material |
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| CN108048831A (en) * | 2017-12-14 | 2018-05-18 | 马鞍山新徽铝业有限公司 | A kind of method that aluminium alloy blacks |
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