【摘要】：作為最輕的金屬結(jié)構(gòu)材料,鎂合金材料具有比強(qiáng)度、比剛度高,電磁屏蔽性能好等一系列優(yōu)點,這些優(yōu)異的特性使其在汽車工業(yè)、航空航天、電子制造業(yè)、通訊行業(yè)等領(lǐng)域也得到越來越廣泛的使用,但鎂合金較差的耐蝕性能影響其應(yīng)用發(fā)展。達(dá)克羅涂層作為一種廣泛應(yīng)用于鋼鐵材料的綠色清潔型表面處理技術(shù),然而當(dāng)達(dá)克羅技術(shù)應(yīng)用于鎂合金時,由于鎂合金化學(xué)活性高,在成膜過程中達(dá)克羅涂液中的酸性物質(zhì)優(yōu)先與鎂反應(yīng)生成疏松的腐蝕物,不能形成致密的阻擋層。本文采用掃描電鏡(SEM)及能譜儀(EDS)、X射線衍射儀(XRD)、極化曲線測試及電化學(xué)阻抗譜、浸泡實驗、鹽霧試驗等多種分析測試手段,以AZ31鎂合金板材為實驗材料,在優(yōu)化鎂合金達(dá)克羅涂層成分配比的基礎(chǔ)上,研究了不同硼酸含量對達(dá)克羅膜層成分、組織形態(tài)結(jié)構(gòu)及耐蝕性能的影響,并制備了硅烷-達(dá)克羅復(fù)合涂層以進(jìn)一步提高其耐腐蝕性能,得到的主要結(jié)論為:鎂合金達(dá)克羅涂層優(yōu)化成分配比為:片狀鋅粉的含量為300g/L,鉻酐含量為80g/L;乙二醇含量為180ml/L。增稠劑為羥乙基纖維素;p H值調(diào)節(jié)劑為Zn O;消泡劑為異辛醇。最佳的固化工藝為80℃保溫10min,升溫至300℃固化30min。制備的鎂合金達(dá)克羅涂層主要由Zn、Mg及其鉻酸化合物Mg Cr O_4和氧化物Zn O、Mg O、Cr_2O_3、Cr O_3組成。涂層厚度在10μm左右。添加硼酸取代部分鉻酸后,涂層中出現(xiàn)硼的氧化物B_2O_3,隨著硼酸含量的增加,Mg、Mg Cr O_4含量降低,Cr_2O_3及Cr O_3的含量先上升后降低,在添加2%硼酸時含量最高;此時涂層表面裂紋孔洞的數(shù)量最少,涂層致密性最好。隨著硼酸含量的增加使涂層腐蝕電位降低,自腐蝕電流密度先減小后增大,硼酸含量為2%時腐蝕電流密度最小,比未添加硼酸時降低一個數(shù)量級。同時,涂層的電荷轉(zhuǎn)移電阻值R_(ct)先升高后降低,含量為2%時達(dá)到最大值。添加2%硼酸涂層鹽霧腐蝕75h時出現(xiàn)明顯的腐蝕現(xiàn)象。在達(dá)克羅涂層上二次涂覆硅烷涂料制備了硅烷-達(dá)克羅復(fù)合涂層。涂層中出現(xiàn)Si O_2和Zn_2Si O_4新相。復(fù)合涂層結(jié)合緊密,厚度在20μm左右。與達(dá)克羅涂層相比,復(fù)合涂層極化電阻R_p值由208.1Ω·cm~2提高到770.3Ω·cm~2,腐蝕電流密度I_(corr)大小由5.068×10~(-5)A·cm~(-2)減小至2.716×10~(-6)A·cm~(-2),電荷轉(zhuǎn)移電阻R_(ct)由107.5Ω·cm~2提高到217.2Ω·cm~2。與硼酸取代部分鉻酸的達(dá)克羅涂層相比,復(fù)合涂層的耐鹽霧腐蝕性顯著增強(qiáng)。
[Abstract]:As the lightest metal structure material, magnesium alloy material has a series of advantages, such as specific strength, high specific stiffness, good electromagnetic shielding performance and so on. Communication industry and other fields have been more and more widely used, but the poor corrosion resistance of magnesium alloy affects the development of its application. Dacromet coating is a kind of green clean surface treatment technology widely used in iron and steel materials. However, when Dacromet technology is applied to magnesium alloy, the chemical activity of magnesium alloy is high. In the process of film formation, the acidic substance in the Dacromet solution preferentially reacts with magnesium to form a loose corrosion substance, which can not form a dense barrier layer. In this paper, (SEM) and (EDS), X ray diffractometer of scanning electron microscope (SEM) and (EDS), X ray diffractometer (EDS), X) were used to measure the polarization curve and electrochemical impedance spectrum (EIS), immersion test, salt spray test and so on. The AZ31 magnesium alloy sheet was used as the experimental material. The effects of different boric acid content on the composition, microstructure and corrosion resistance of Dacromet coating on magnesium alloy were studied. Silane-Dacromet composite coating was prepared to further improve its corrosion resistance. The main conclusions are as follows: the optimum composition of the coating is: the content of zinc powder is 300 g / L, the content of chromium anhydride is 80 g / L, and the content of ethylene glycol is 180 ml / L. The thickener is hydroxyethyl cellulose; p H value regulator Zn O, and the defoamer is isooctanol. The optimum curing process is 80 鈩，

本文編號：2265661