Preparation method of magnesium alloy surface micro-arc oxidation-tourmaline-doped composite coating
Technical Field
The invention relates to the technical field of material surface treatment, in particular to a preparation method of a magnesium alloy surface micro-arc oxidation-tourmaline-doped composite coating.
Background
The magnesium alloy is used as the lightest metal structure material, and has the advantages of small density, high specific strength, good thermal conductivity, good damping vibration attenuation and biocompatibility and the like, thereby having wide application prospect in the fields of traffic, aerospace, information, medical use and the like. But the standard electrode potential of the magnesium is only-2.37V, the magnesium is a metal with strong electronegativity, and the chemical property of the magnesium is very active; and an oxide film generated on the surface of magnesium in the air is loose and porous, so that the protective capability to a matrix is poor. Therefore, magnesium alloys are not suitable for most corrosive environments, which severely restricts the wide application of magnesium alloys.
Disclosure of Invention
The invention provides a preparation method of a magnesium alloy surface micro-arc oxidation-tourmaline-doped composite coating, aiming at solving the problem that the use of magnesium alloy is influenced by poor corrosion resistance of the magnesium alloy in corrosive media such as humid atmosphere, soil and the like.
The preparation method of the magnesium alloy surface micro-arc oxidation-tourmaline-doped composite coating specifically comprises the following steps:
firstly, magnesium alloy surface pretreatment: polishing the surface of a magnesium alloy test piece by using abrasive paper until no scratch is formed, then soaking the magnesium alloy test piece into an ultrasonic cleaning machine filled with acetone to remove oil for 3-5 min, and naturally drying to obtain a magnesium alloy test piece to be oxidized;
secondly, preparing a micro-arc oxidation coating: placing the micro-arc oxidation electrolyte in a stainless steel electrolytic tank, adopting a bipolar pulse micro-arc oxidation power supply, taking the stainless steel electrolytic tank as a cathode, and taking a magnesium alloy test piece to be oxidized as an anode; placing a magnesium alloy test piece to be oxidized into a micro-arc oxidation electrolyte for stabilization for 3-5 min, turning on a bipolar pulse micro-arc oxidation power supply, oxidizing for 10-15 min under the conditions that the frequency is 200-600 Hz, the duty ratio is 5-10% and the voltage is 400-450V, turning off the bipolar pulse micro-arc oxidation power supply after micro-arc oxidation is finished, obtaining the magnesium alloy test piece subjected to micro-arc oxidation, cleaning for 3-5 times by using distilled water, naturally airing, and placing into a sealing bag for later use;
thirdly, preparing a tourmaline-doped coating: stirring the mixed solution and the silicone-acrylate emulsion on a magnetic stirrer at a speed of 300-600 r/min for 30-50 min to prepare slurry, immersing the magnesium alloy test piece subjected to micro-arc oxidation into the slurry, vertically pulling the magnesium alloy test piece subjected to micro-arc oxidation out of the slurry at a speed of 4-7 cm/min, repeatedly pulling for 2-3 times, and then placing at room temperature for natural drying for 2-3 days to form a coating film, thus obtaining the micro-arc oxidation-tourmaline-doped composite coating on the surface of the magnesium alloy; the mixed solution is formed by mixing a dispersing agent, a defoaming agent, magnesium tourmaline powder and water, wherein the dispersing agent accounts for 0.1-1% of the total mass, the defoaming agent accounts for 0.1-0.5% of the total mass, and the magnesium tourmaline powder accounts for 1-5% of the total mass; the solid content in the silicone-acrylate emulsion is 50 percent; the mass ratio of the mixed solution to the silicone-acrylate emulsion is 1 (1-2).
The invention has the beneficial effects that:
firstly, micro-arc oxidation technology is adopted, and micro-arc discharge is generated by utilizing gas ionization in electrolyte under high pressure, so that an oxide ceramic coating is generated on the surface of AZ31B in situ; then, coating film is formed on the surface of the micro-arc oxidation coating by adopting tourmaline-doped coating to seal the micropores of the micro-arc oxidation coating. The main component of the coating is silicone-acrylate emulsion, which has the advantages of good water resistance, acid resistance, alkali resistance, contamination resistance and the like; the tourmaline can adsorb anions and form a monomolecular film by electrolyzing water, so that the protective effect of the composite coating on the magnesium alloy matrix can be improved.
Drawings
FIG. 1 is a surface topography map of a magnesium alloy test piece after micro-arc oxidation obtained in the second step of the embodiment;
FIG. 2 is a surface topography map of the magnesium alloy surface micro-arc oxidation-tourmaline-doped composite coating obtained in the third step of the embodiment.
Detailed Description
The first embodiment is as follows: the preparation method of the magnesium alloy surface micro-arc oxidation-tourmaline-doped composite coating comprises the following steps:
firstly, magnesium alloy surface pretreatment: polishing the surface of a magnesium alloy test piece by using abrasive paper until no scratch is formed, then soaking the magnesium alloy test piece into an ultrasonic cleaning machine filled with acetone to remove oil for 3-5 min, and naturally drying to obtain a magnesium alloy test piece to be oxidized;
secondly, preparing a micro-arc oxidation coating: placing the micro-arc oxidation electrolyte in a stainless steel electrolytic tank, adopting a bipolar pulse micro-arc oxidation power supply, taking the stainless steel electrolytic tank as a cathode, and taking a magnesium alloy test piece to be oxidized as an anode; placing a magnesium alloy test piece to be oxidized into a micro-arc oxidation electrolyte for stabilization for 3-5 min, turning on a bipolar pulse micro-arc oxidation power supply, oxidizing for 10-15 min under the conditions that the frequency is 200-600 Hz, the duty ratio is 5-10% and the voltage is 400-450V, turning off the bipolar pulse micro-arc oxidation power supply after micro-arc oxidation is finished, obtaining the magnesium alloy test piece subjected to micro-arc oxidation, cleaning for 3-5 times by using distilled water, naturally airing, and placing into a sealing bag for later use;
thirdly, preparing a tourmaline-doped coating: stirring the mixed solution and the silicone-acrylate emulsion on a magnetic stirrer at a speed of 300-600 r/min for 30-50 min to prepare slurry, immersing the magnesium alloy test piece subjected to micro-arc oxidation into the slurry, vertically pulling the magnesium alloy test piece subjected to micro-arc oxidation out of the slurry at a speed of 4-7 cm/min, repeatedly pulling for 2-3 times, and then placing at room temperature for natural drying for 2-3 days to form a coating film, thus obtaining the micro-arc oxidation-tourmaline-doped composite coating on the surface of the magnesium alloy; the mixed solution is formed by mixing a dispersing agent, a defoaming agent, magnesium tourmaline powder and water, wherein the dispersing agent accounts for 0.1-1% of the total mass, the defoaming agent accounts for 0.1-0.5% of the total mass, and the magnesium tourmaline powder accounts for 1-5% of the total mass; the solid content in the silicone-acrylate emulsion is 50 percent; the mass ratio of the mixed solution to the silicone-acrylate emulsion is 1 (1-2).
The second embodiment is as follows: the first difference between the present embodiment and the specific embodiment is: in the first step, the magnesium alloy test piece is AZ31B magnesium alloy, and the chemical components are as follows: 84.43 wt% Mg, 2.56 wt% Al, 0.81 wt% Zn, 5 wt% Mn, 7.2 wt% Si. The rest is the same as the first embodiment.
The third concrete implementation mode: the present embodiment differs from the first or second embodiment in that: in the step one, the grinding is carried out by sequentially adopting 200-1000-mesh SiC sand paper. The others are the same as in the first or second embodiment.
The fourth concrete implementation mode: the difference between this embodiment mode and one of the first to third embodiment modes is: the formula of the micro-arc oxidation electrolyte in the step two is as follows: 15 g/L-25 g/L sodium silicate, 5 g/L-10 g/L sodium hydroxide, 10ml/L-20ml glycerol and 1 g/L-3 g/L sodium fluoride. The rest is the same as one of the first to third embodiments.
The fifth concrete implementation mode: the difference between this embodiment and one of the first to fourth embodiments is: and step three, the mixed solution is prepared by putting the dispersing agent, the defoaming agent and water into a mixing tank, uniformly stirring, adding the magnesium tourmaline powder, and stirring for 20-30 min on a magnetic stirrer at the speed of 800-1000 r/min. The rest is the same as one of the first to fourth embodiments.
The sixth specific implementation mode: the difference between this embodiment and one of the first to fifth embodiments is: the dispersant is SN-5027, and the defoaming agent is SN-154. The rest is the same as one of the first to fifth embodiments.
The following examples were used to demonstrate the beneficial effects of the present invention:
the preparation method of the magnesium alloy surface micro-arc oxidation-tourmaline-doped composite coating specifically comprises the following steps:
firstly, magnesium alloy surface pretreatment: polishing the surface of an AZ31B magnesium alloy test piece by using sand paper until no scratch exists, then immersing the AZ31B magnesium alloy test piece into an ultrasonic cleaning machine filled with acetone to remove oil for 3min, and naturally airing to obtain a magnesium alloy test piece to be oxidized;
secondly, preparing a micro-arc oxidation coating: placing the micro-arc oxidation electrolyte in a stainless steel electrolytic tank, adopting a bipolar pulse micro-arc oxidation power supply, taking the stainless steel electrolytic tank as a cathode, and taking a magnesium alloy test piece to be oxidized as an anode; placing a magnesium alloy test piece to be oxidized into a micro-arc oxidation electrolyte for stabilization for 3min, turning on a bipolar pulse micro-arc oxidation power supply, oxidizing for 10min under the conditions of 400Hz frequency, 8% duty ratio and 400V voltage, turning off the bipolar pulse micro-arc oxidation power supply after micro-arc oxidation is finished, obtaining the magnesium alloy test piece after micro-arc oxidation, cleaning for 3 times by using distilled water, naturally airing, and placing into a sealing bag for later use; the micro-arc oxidation electrolyte contains 20g/L of sodium silicate, 5g/L of sodium hydroxide, 10ml/L of glycerol and 1g/L of sodium fluoride;
thirdly, preparing a tourmaline-doped coating: stirring the mixed solution and the silicone-acrylate emulsion on a magnetic stirrer at a speed of 500r/min for 30min to prepare slurry, immersing the magnesium alloy test piece subjected to micro-arc oxidation into the slurry, vertically pulling the magnesium alloy test piece subjected to micro-arc oxidation out of the slurry at a speed of 5cm/min, repeatedly pulling for 2 times, and naturally drying at room temperature for 2 days to form a coating film to obtain the magnesium alloy surface micro-arc oxidation-tourmaline-doped composite coating; the mixed solution is formed by mixing SN-5027 dispersing agent, SN-154 defoaming agent, magnesium tourmaline powder and water, wherein the SN-5027 dispersing agent accounts for 0.6% of the total mass, the SN-154 defoaming agent accounts for 0.4% of the total mass, and the magnesium tourmaline powder accounts for 2% of the total mass; the solid content in the silicone-acrylate emulsion is 50 percent; the mass ratio of the mixed solution to the silicone-acrylate emulsion is 1: 2.
The surface appearance of the obtained micro-arc oxidation ceramic coating is shown in figure 1, and the micro-arc oxidation coating is in a porous honeycomb structure which has strong adsorption capacity to tourmaline-doped paint. Due to microThe arc oxidation coating is formed by in-situ growth on the surface of the AZ31B magnesium alloy substrate, so the coating is firmly combined with the substrate, has high hardness and is easy to control the thickness. The surface appearance of the prepared tourmaline-doped coating film is shown in figure 2, the tourmaline particles can be seen to be distributed in the coating film, the coating film is uniform and compact, and the micro-arc oxidation film micropores are completely sealed. The main component of the coating is silicone-acrylate emulsion, which has the advantages of good water resistance, acid resistance, alkali resistance, contamination resistance and the like; tourmaline in the coating film is a cyclic silicate mineral mainly containing boron, has permanent electric field and self-polarization characteristics, and can electrolyze water molecules adsorbed on the surface under the action of weak current to generate OH-Combined with water molecules to form H3O2 -A monomolecular film for isolating the surrounding medium from the coating film. The electrochemical corrosion detection result shows that: the corrosion potential and the self-corrosion current density of the AZ31B magnesium alloy substrate are respectively-1.55V and 6.46 multiplied by 10-3A/cm2(ii) a The corrosion potential and the self-corrosion current density of the tourmaline-doped coating film are respectively-1.49V and 1.14 multiplied by 10-5Acm2. Compared with an AZ31B magnesium alloy matrix, the corrosion potential of the micro-arc oxidation-tourmaline composite coating prepared by the invention is improved by 60mV, the self-corrosion current density is reduced by 2 orders of magnitude, and the corrosion resistance of the AZ31B magnesium alloy is effectively improved.