자동차용 난방기의 부식거동에 관한 연구

Abstract

최근, 선박 및 자동차용 열교환기인 냉각기와 방열기의 재질로 알루미늄합금재(Al-alloy)의 사용이 증가하고, 자동차는 엔진의 냉각과 공기의 원활한 순환을 위하여 많은 열교환기가 사용되고 있으며 이것들은 다른 분야에 사용되고 있는 열교환기에 비하여 경량, 소형화의 요구가 대단히 크고 가벼우면서 열전도성이 우수한 알루미늄은 자동차용 열교환기에 적당한 재료로서 대부분의 자동차용 열교환기에 폭넓게 이용되며 앞으로도 사용 예가 확대되면서 Al합금재로 제작되는 선박 및 자동차용 열교환기에 Al합금재보다 귀전위금속인 동, 황동 및 스테인레스강 등의 이종금속을 사용하는 경우도 있으나 이들 이종금속에 의한 Al합금의 전지작용부식이 촉진되고 있다. 그러나 본 논문은 자동차용 냉난방기의 재료로 사용되는 알루미늄 합금재와 황동의 부식거동을 연구하기 위하여, 난방수의 비저항에 따른 용액 중에서 Al 합금재의 전기화학적 분극시험 및 황동과 이종금속조합된 Al합금재의 이종금속접촉부식실험을 실시하여, 난방수의 비저항에 따른 Al합금재와 황동의 전면부식거동에 대해 내식성 평가와 국부부식거동에 대해 고찰하고, 특히 황동과 조합된 Al합금재의 이종금속접촉부식특성을 구명함으로써 Al합금재를 사용하는 자동차용 냉난방기의 부식과학, 최적화 설계 및 보수 유지의 기초자료로 활용하는데 기여할 것으로 사료된다.

Recently, Al-alloy has been increasing for the cooling system and radiator of the ships and automobile materials. Especially, automobile uses lots of heat exchangers because of cooling engine and smooth running rotation, those are needed to be more miniaturized and light. Also, the heat conductivity of aluminum is excellent. It has been used in automobile' air conditioner system since 1960. Heat exchanger materials for ships and automobile are using more brass, stainless steel than Al-alloy. Therefore, galvanic cell is formed with Al-alloy and Cu for automobile radiator material, and corrosion of Al-alloy is accelerated. Industrial development and income increase causes rapid increase in using fossil energy like coal, petroleum and natural gas, and it results in accelerating environmental pollution. Specially, fresh water like stream and river water is acidified and specific resistance is decreased. Therefore, corrosion damage is accelerated in radiator for automobile under the acidified water. In the study, so as to investigate the corrosion behavior of Al-alloy, the electrochemical polarization test of Al-alloy with changing specific resistance and galvanic corrosion test of Al-alloy coupling with brass were carried out. The main results obtained are as follows ; 1) As the specific resistance decreases, the slope of the linear polarization behavior is on the decrease, and the polarization resistance decreases. 2) As the specific resistance decreases, the open circuit potential of Al-alloy is less noble, and the corrosion-resistance for uniform corrosion is on the decrease. 3) Only passive behavior appears in the heating water which is in the high specific resistance of 140000 Ω?cm, by the contrast, a pitting potential is getting fast in the specific resistance under the 6200 Ω·cm. 4) In the heating water which is in the high specific resistance of 140000 Ω·cm, cyclic loop of Al-alloy has the negative hysteresis loop at reverse scan anodic polarization curves, if it is affected with the pitting and crevice corrosion, the passive film of Al=alloy destroyed at positive scan may be repaired 5) As the specific resistance decreases from the heating water of specific resistance of 6200 Ω·cm, cyclic loof of Al-alloy shows the positive hysteresis at reverse scan anodic polarization curve and corrosion current density of cyclic increases. Therefore it may be sensitive for pitting and crevice corrosion. 6) Because the average electrode potential of brass is higher than that of Al-alloy, the brass operates with the cathode, at Al-alloy operates with the anode. So, galvanic corrosion will occur. 7) In the study, under the specific resistance of 500 Ω·cm mixed 30% anti-freeze solution, the uniform corrosion, pitting and galvanic corrosion of Al-alloy is decreased.