Study Of Corosion Behavior Of Magnesium Alloys In Commercial Engine Coolant

In this paper, through Immersion, electrochemical test, XPS analysis,ASTM D 1384 measurement and etc., the corrosion behavior of AM-SC1,AZ91D and NZK magnesium alloys in CALTEX coolant with KFaddition were studied.In immersion test, it was found that, increasing the KF addition inCALTEX coolant, the corrosion rates of the three alloys increased. Theinhibitive effect of KF on AM-SC1 and NZK alloys was significant,while not such obvious on AZ91D alloy.The results from electrochemical measurement showed that, (1) theincreasing addition of KF increases the open circuit potential, equilibriumpotential and resistivity of AM-SC1 and NZK alloy. (2) KF has slighteffect on the open circuit potential, equilibrium potential and resistivity ofAZ91D alloy.It was inferred from SEM test that while in CALTEX coolantsolution containing KF, (1) the film formed on the surface of AZ91Dalloy is mainly consist of round particles of MgF2 phase, and thethickness of the coating is about 1μm. (2) the film formed on the surface of AM-SC1 alloy is mainly consist of cubic particles of Mg(OH)2 andMgF2 phases, and the thickness of the coating is about 1μm. (3) the filmformed on the surface of NZK alloy is mainly consist of round particlesof MgF2 phase and the thickness of the coating is about 1.5μm.The result of ASTM D 1384 measurement turned out to be that, onlythe corrosion rates of AZ91D alloy in CALTEX coolant solutioncontaining 0.5wt.%KF and 1wt.%KF were above the acceptable thresholdfor magnesium alloys.After the pre-treatment and surface pretreatment, the results ofASTM D 1384 test turned out to be that (1) based onCALTEX+0.5wt%KF solution, after the pretreatment, corrosion rates ofAZ91D and NZK in immersion test at 25℃after addition of variousconcentration of copper inhibitor were higher than those of the normaltest, (2) after the surface pretreatment which means firstly immersing thealloys in different chemical solutions, corrosion rates of three alloys inASTM D 1384 test could not at the same qualify the needs for thethreshold (0.67mg/cm2/week).