【作者】 詹柏林；

【导师】 朱有兰；

【作者基本信息】 广东工业大学 ， 材料学， 2007， 硕士

【摘要】 换热器在工业生产以及日常生活中的应用非常广泛。但是，换热器表面的腐蚀问题仍旧没有得到很好的解决，特别是在工业生产领域。电镀和化学镀，作为一种表面处理技术，可以获得具有优良的耐腐蚀性能的非晶态镀层。其工艺设备简单，易于控制和掌握，生产镀层成本低等特点，而且适用于形状复杂的零件，非常适合用于解决换热器表面腐蚀问题。目前已经在逐步采用。本文针对目前低温电镀Ni-P合金形成非晶难、镀层耐蚀性差和化学镀Ni-P合金镀液稳定性差、镀速低、镀层致密性差的特点，通过添加适量的氯化铵和添加剂，采用正交试验研究方法，实验结果以检测镀层孔隙率、微观表面裂纹、中性盐雾腐蚀实验、XRD晶体结构分析和EDS成分分析等手段，以镀层孔隙率、微观表面裂纹、晶体结构和镀液稳定性为主要参考指标，比较系统地研究了在廉价换热器用材Q235钢基体上，以硫酸镍为主盐，以次磷酸钠作为镀层磷元素来源和催化还原作用在低温下电镀和化学镀过程中的配方和工艺参数。为高氯化铵浓度下，在Q235钢基体上低温电镀耐蚀性优良的非晶态Ni-P镀层和化学镀非晶态Ni-P镀层的行为规律奠定了基础。通过研究得到以下结论：1．电镀非晶态Ni-P合金各因素对镀层影响规律如下：①NH₄Cl用量大小的影响规律：当NH₄Cl用量高于0.6mol／L时，45℃下电镀Ni-P，X射线衍射检测证明镀层为非晶态结构；NH₄Cl加入量越多，所获镀层孔隙率越高，裂纹也越严重；②PH值大小的影响：PH≤2时，会导致镀不上；当PH值在3～4时可以保证顺利获得镀层。PH值对镀层孔隙率和裂纹影响最大的因素。PH越小，所获镀层孔隙率越小，而裂纹却越明显；③温度T：在25～45℃低温下，温度对镀层孔隙率、裂纹影响不大；当施镀温度大于45℃后，温度越高，镀层孔隙率越低，裂纹不断消失，当镀温达75℃时，镀层裂纹几乎完全消失；④电流密度Ⅰ：电流密度越大，所获镀层孔隙率就越高；当电流密度Ⅰ=1.5 A/dm²时，所获镀层孔隙率最低，裂纹最轻。2．在没有添加剂参与条件下，高NH₄Cl浓度所获非晶态Ni-P镀层表面裂纹比较严重，孔隙率较高，耐蚀性能差。采用糖精、十二烷基硫酸钠、1，4丁炔二醇等添加剂，对配方和工艺经过正交优化后，消除了镀层裂纹、降低了镀层孔隙率，大大提高了非晶态镀层的耐蚀性能。最终优化工艺配方为：NiSO₄·6H₂O=40g／L、NaH₂PO₂·H₂O=30g／L、H₃BO₃=15g／L、NH₄Cl=32g／L、糖精0.12g／L、12烷基硫酸钠0.03g／L、1，4丁炔二醇0.1g／L、施镀温度T=45℃、电流密度Ⅰ=1.5 A／dm²、PH=4；3．镀层EDS分析表明：电沉积和化学沉积非晶态Ni-P合金镀层是个动态变化的过程。电沉积过程中，所获镀层越靠近基体，镀层中P含量越低；在最终优化工艺配方所获镀层由表面到镀层中心再到靠近基体部位P元素质量百分比wt％变化情况为：6.61％→7.18％→8.73％，镀速为25.02um／h；化学沉积过程中，镀层中P含量成波动起伏变化，由表面到镀层中心再到靠近基体部位P元素质量百分比wt％变化情况为：10.79％→10.97％→10.70％，镀速为9.00um／h；4．高NH₄Cl浓度不会影响化学镀非晶态Ni-P合金的规律。在高NH₄Cl浓度下，施镀温度，PH值对镀层性能的影响几乎与目前化学镀非晶态Ni-P合金镀层的规律一样；5．化学镀非晶态Ni-P合金中，施镀温度T、PH值和添加剂对镀层性能影响规律如下：①施镀温度T的影响规律：T越高，镀速越快，镀层显微硬度越高，孔隙率越低，镀层耐蚀性能越好，但镀液的稳定性越差；②：PH值的影响规律：PH值越高，镀速越快，镀层显微硬度越高，镀液稳定性越差；从镀液稳定性、镀速和镀层耐蚀性能综合考虑，实验得出在NiSO₄·6H₂O=40g／L、H₃BO₃=15g／L、NaH₂PO₂·H₂O=30 g／L、NH₄Cl=0.6 mol/L、PH=4、T=85℃工艺配方下，可获优良的耐蚀镀层；③添加剂的影响规律：添加剂用量越多，镀速越慢，镀液稳定性越高；它的适量加入能降低镀层硬度，降低镀层孔隙率，使镀层在阳极极化曲线中表现出更宽的稳定钝化区，二次钝化中的钝化电压和钝化电流更低，提高镀层耐蚀性能；三种添加剂当中，糖精的用量影响最大，其次是1，4丁炔二醇，而十二烷基硫酸钠的加入量影响最小；从镀液稳定性、沉积速度和镀层耐蚀性综合考虑，05组实验为最佳配方，即：NiSO₄·6H₂O=40g／L、H₃BO₃=15g／L、NaH₂PO₂·H₂O=30g／L、NH₄Cl=0.6mol／L、PH=4、镀温=85℃、糖精=1.0 g／L、十二烷基硫酸钠=0.15g／L、1，4丁炔二醇=0.3 g／L；6．阳极极化曲线测定表明，Q235钢经低温电镀和化学镀非晶态Ni-P合金镀层后，其耐蚀性能大大得到提高。但化学镀的提高得多。镀层使Q235钢在wt％=42％LiCl中初始阶段便进入稳定的钝化区，由于镀层中P含量的波动，使Q235钢在阳极极化曲线中出现二次钝化和三次钝化。更多还原

【Abstract】 Heat exchangers are used extensively in industry and our daily life. But the corrosion ofheat exchangers still can not be solved well, especially in industry. The greatanticorrosion amorphous coating can be made by means of plating and electroless. Assurface treatment technologies, plating and electroless have more advantages over othertechnologies, such as simple equipments processes, esay to control and low-cost to getcoatings and so on, and the what’s more, they can be used to the complex shape parts.So they are quite suitable to solve the corrosion of heat exchangers, and they have beenused gradually.In this paper, by adding enough more ammonium and proper plating agent, usingorthogonal-design experiments, examining porosity of coating, microsurface crack,microhardness, crystal structure etc. Target of the main examine by according toporosity of coating, microsurface crack and anticorrosion ability. The processparameters and contents of plating and electroless amorphous Ni-P coating on thesurface of Q235 steel are systemically studied in low temperature, using NiSO₄ as mainsalt and reducing agent NaH₂PO₂ as P element source. Theoretic and practical basis ofmanufacturing excellent anticorrosion amorphous Ni-P coating on Q235 steel surface inthe low temperature is made in the paper. The regulars of electroless amorphous Ni-Pcoating on the surface of Q235 steel in high ammonium condition are also studied. Thestudy results as follow:1. The factor effect regulars of Electroplating Ni-P amorphous alloy coating are asfollows:①NH₄Cl amount: XRD test showed that the structure of coating is amorphouswhen the amount of NH₄Cl is over 0.6mol/L; the more of NH₄Cl amount, themore serious the coating porosity and crack is;②Effect regular of PH: coating can’t be made when PH value is low 2, butbetween 3 to 4; PH has great effect on coating’s porosity and crack: the lowerPH is, the lower the porosity is, but the crack of the coating is more serious. ③Temperature T: temperature has little effect on porosity and crack of coating,when it betweens 25 degree to 45 degree. However when the temperature isover 45 degree, the temperature is higher, the porosity is lower, and the crack isless serious, when the temperature is high up to 75 degree, the crack can bedisappeared.④Current densityⅠ: the higher current density is, the more porosity will be;porosity is lowest and crack is lest when current density is 1.5 A/dm²;2. Under the condition of no additives, corrosion resistance of the amorphous coatingmanufactured by high concentration of NH₄Cl is bad because of it serious crack andhigh porosity. Ni-P amorphous coating corrosion resistance is improved greatlyafter 2 times orthogonal experiments by adding additives of saccharin, sodiumdodecyl sulfate and 1, 4 butynediol properly. Optimal formulation and processes asfollow:NiSO₄·6H₂O=40g/L, NaH₂PO₂·H₂O=30g/L, H₃BO₃=15g/L, NH₄Cl=32g/L, saccharin=0.12g/L, sodium dodecyl sulfate=0.03g/L, 1, 4 butynediol=0.1 g/L, temperatureT=45℃, current densityⅠ=1.5 A/dm²;3. EDS analysis of the coating made by optimal formulation and processes certificated:the courses of electroplating and chemical plating Ni-P amorphous are dynamic. Inelectroplating course, the more close to the matrix, the lesser of P content in thecoating; from surface to the centre, and from the centre to the part near to the matrix,the weight percentage of P ranges 6.61%→7.18%→8.73%, the deposition velocityis 25.02um/h; In the course of chemical deposition, P element is fluctuating changedin the coating, from surface to the centre, then from the centre to the part near to thematrix, P element weight percentage ranges 10.79%→10.97%→10.70%, thedeposition velocity is 9.00um/h;4. The regulars of electroless Ni-P amorphous coating almost keep the same as theregulars of electroless Ni-P amorphous coating without the high concentration ofNH₄Cl. The influence laws of temperature and PH in chemical plating Ni-Pamorphous coating under the high concentration of NH₄Cl are the same as thecommon chemical plating Ni-P amorphous coating laws; 5. plating temperature, pH value and performance additives for Electroless Ni-Pamorphous alloy coatings effects are as follows:①temperature T: The higher the temperature, the faster the plating velocity, thehigher the coating hardness, and the lower the porosity, so the better corrosionresistance, However, the poorer the stability of the bath;②PH value: The higher the pH value, the faster the plating velocity, and thehigher the coating hardness, but the worse the bath stability; the bath stability;take the plating velocity and the corrosion resistance into account, experimentcame to an good conclusion: NiSO₄·6H₂O=40g/L、H₃BO₃=15g/L、NaH₂PO₂·H₂O=30 g/L、NH₄Cl=0.6 mol/L、PH=4、T=85℃;③Additive: the more, the Additives, the slower the deposition velocity, the higherthe stability of the bath; It can be appropriate to reduce the hardness of thecoatings, reduce porosity. It makes anode polarization curve has broaderpassivasion, lower passivasion voltage and passivasion current in secondpassivasion, improve coating corrosion resistance; among the three additives,the amount of saccharin has the greatest effect on bath, the second one is 1, 4butynediol’s, and the last one is sodium dodecyl sulfates; taking the stability,deposition velocity and anticorrosion property into account, the optimumprocesses and formula is as follow: NiSO₄·6H₂O=40g/L、H₃BO₃=15g/L、NaH₂PO_·H₂O=30g/L、NH₄Cl=0.6mol/L、PH=4, T=85℃、saccharin=1.0 g/L、sodium dodecyl sulfate=0.15g/L、1, 4 butynediol=0.3 g/L;6. Anode polarization curves tests show: Q235 steel corrosion resistance has greatlyimproved after low temperature electroplating and electroless amorphous Ni-Palloy coating; electroless amorphous Ni-P do better. Ni-P alloy coating makesQ235 steel enters a stable passivation district at the beginning stage in wt%=42%LiCl solution; Q235 steel appears second passivation and third passivation in theanode polarization curves because of the P fluctuation in the coating.更多还原