| Magnesium alloy has been widely used in many fields attributed to its series of merits, such as light weight, high strength, super plastic deformation, good cast ability, good weld ability, preferred impact shock absorption, thermal conductivity, electrical conductivity and toxic-free performance, recycling and so on. However, the poor corrosion resistance of magnesium alloy has seriously limited its further application. Therefore, it is very important to increase the corrosion resistance of magnesium alloy. The microstructure and corrosion resistance property of as-cast AZ61-mY and ZA84-nCa alloy were studied by using OM, SEM, XRD and electrochemical testing method. Results showed that:(1)After adding Y to AZ61alloy, AZ61-mY alloy consists of a-Mg, β-Mg17Al12and A12Y phase.When the amount of Y addition to AZ61alloy changing, the morphology and distribution of the second (3-Mg17Al12phase have taken significant changes. When Y addition reached1.0wt.%, P-Mg17Al12phase was more evenly dispersed accompanied with the growing number of A12Y phase.(2)The corrosion resistance property of as-cast AZ61alloy was studied by the method of static weight loss with observing corrosion morphology of the alloy and electrochemical test. Results showed that adding proper element Y can increase the corrosion resistance property of AZ61alloy.The static weight loss corrosion test results showed that the average corrosion rate of AZ61-(0～1.5)Y alloys immersed in3.5%NaCl solution for5days is11.41692,2.85699,2.29968and4.22517g/(m2·h), respectively. The observing of corrosion morphology of AZ61alloy after the static weight loss test for48h were depicted as follows:AZ61alloy without Y addition was roughly corroded entirely, and the corrosion degree was so serious with a lot of deep corrosion pits were clearly seen out. On the contrary, AZ61alloy with1.0wt.%Y addition has the lowest corrosion rate. Addition of Y to AZ61alloy can obviously improve the corrosion resistance property.The electrochemical corrosion test showed that element Y can decrease the corrosion current density of AZ61alloys. The corrosion current density of AZ61alloys was relatively higher in the first place, and then it went down with the increasing of element Y addition. The corrosion current density of the AZ61alloy with Y addition is lower than that of alloy without Y addition. When Y in the addition of1.0wt.%, corrosion current density of AZ61alloys is0.6923mA/cm2. It is the lowest corrosion current density value of this polarization test.(3) After adding Ca to ZA84alloy, the microstructure has great re fine effects. This can be owned to the evenly dispersed morphology of the τ-Mg32(Al,Zn)49phase. There was no new phase formed in ZA84alloy with Ca addition.(4)The corrosion resistance property of as-cast ZA84-nCa alloy was investigated by using electrochemical test, static weight loss method with observing the corrosion morphology of alloys. Of all the experimental data of the four kinds of alloys, ZA84-0.3Ca alloy has the best corrosion resistance property.The static weight loss test results showed that corrosion rate of ZA84alloy with Ca addition is separately decreased in the number of39.6%,24.9%and15.9%. ZA84-0.3Ca alloy has the lowest corrosion rate among the four kinds of alloy. The macroscopic corrosion morphology of the cast ZA84-nCa alloys immersed in3.5%NaCl solution for16h shows that the graveness corrosion extent is ZA84alloy without Ca addition and only local area was found to be uncorroded. The surface of ZA84alloy with Ca addition can be seen a little pitting corrosion, the lightest surface corrosion degree is ZA84-0.3Ca alloy.The electrochemical corrosion test showed that corrosion potential curve of the alloys moved to positive direction after adding Ca to ZA84alloy. Corrosion current density of the adding (0.3-0.9)Ca alloys is separately44.1%,25.3%and20.9%lower than that of ZA84alloy without Ca addition. |
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