Research On The Corrsion Behavior Of AZ91+x%La Alloy

In the context of resource crisis and environment pollution become more serious, magnesium and magnesium alloy processing performance of its low density, high specific strength, good and can be recycled and other excellent characteristics has gradually become the light metal material transportation, communications and aerospace fields, known as the "green engineering materials in twenty-first Century".Recent studies have found that, AZ91+RE magnesium alloy, which have the advantages of easy casting processing, high strength, low cost etc, have been widely applied to various mechanical parts. However, because of the low electrode potential (-2.73V), activity in chemistry, the magnesium alloys are easily formed the original battery with other elements or inclusions, which can cause galvanic corrosion on the surface. In this way, it is not easy to form a stable protective film and restrict its application in engineering.At present, one of the main reasons leading to the slow development of magnesium alloy application is not well solved the problem of the poor corrosion resistance. Therefore, research on the corrosion mechanism, analysis, study and master the magnesium alloy to constantly enrich and improve the theory of corrosion of magnesium alloy research is to improve the corrosion resistance of magnesium alloy, an important way to expand the scope of application of magnesium alloy industry.Therefore, this study as a basic research link to improve corrosion resistance of magnesium alloy rare earth, with industrial AZ91and pure La as raw materials, AZ91alloy samples with different La content were prepared. By static weight loss test, electrochemical and salt spray corrosion method for determination of AZ91+x%La (x were0,0.063,0.165,0.432,0.646) and the corrosion resistance of the alloy, based on OM, SEM, SEM and XRD diffraction analysis, determination and characterization of AZ91+x%La alloy sample structure, corrosion morphology, corrosion products; and based on the experimental phenomena, corrosion morphology characterization of analysis results and experimental data to establish the dynamic model of the static weight loss corrosion reaction process of AZ91alloy. The results of corrosion coefficient K and microscopic examination of the model to measure the apparent, analysis, research on La content, grain size, phase morphology on corrosion resistance of AZ91, study, mechanism of the corrosion resistance of magnesium alloys to improve. The experimental data provide a basis for enriching and developing the corrosion mechanism and expand the scope of application of magnesium alloy.The experimental results and theoretical analysis showed:1. In the static weight loss test, with increase of the content of La, in a certain range, the corrosion rates of AZ91magnesium alloys decrease and the corrosion resistance is improved. However, the content of La increases future, the corrosion rate increases obviously, this indicates that the corrosion resistance has decreased. When the La content is0.165%, the corrosion rate of AZ91alloy decreases to2mg·cm-2d-1from the original8mg·cm-2·d-1. The corrosion products are mainly Mg(OH)2、Mg6Al2(OH)18·5H2O and a little Mg17Al12。2. In electrochemical experiments, with increase of the content of La, in a certain range, the corrosion potential of AZ91magnesium alloys is improved and the corrosion current is reduced. However, the content of La increases future, the corrosion potential decreases and the corrosion current increases obviously. When the La content is0.165wt.%, the corrosion potential of AZ91alloy increases to-1.328V from-1.400V, and the corrosion current of AZ91alloy decreases to0.014mA from0.527mA.3. In salt spray corrosion test, the corrosion degrees on the surface of AZ91alloys with different content of La are lower than that without rare La. Especially, the corrosion on the surface of No.3alloy (with0.165wt.%La) is lightest and the corrosion resistance is best among the alloys.4. The kinetics results show that:the constant of apparent corrosion rate is affected by grain size (d) and La content. Their relationship is described ask=0.411nd-1.3andk=0.36exp(-25La%)+0.22,respectively. The maximum and minimum value of k is0.58μm/h and0.17μm/h respectively. The reason for decrease of k is that trace La refines the grain size, chances the distribution of β phase, and generates different forms of Al11La3phases. Corrosion protection film is formed in the area near rare earth-enriched phase. The corrosion behavior is turned into filiform corrosion from pitting corrosion, indicating an improvement of corrosion resistance of AM60alloy.5. Trace La element to improve the mechanism of the corrosion resistance of AZ91alloy can be summarized as follows:the trace La grain refinement, change the beta phase (Mg17Al12) and Al11La3phase distribution method is equivalent to increase corrosion resistance, to improve the corrosion potential, lower corrosion current; solidification segregation in Al11La3around the La atom, change the domain AZ91alloy nearby electronic as cloud density, and corrosion products on the surface of alloy to form a protective film, the pitting corrosion to reduce the corrosion rate of the role of filiform corrosion play.