Volta Potential Analysis of Intermetallics in 7A52 Aluminum Alloy

In order to study the effect of intermaetallics on the corrosion behaviour of 7A52 aluminum alloy, the alloy was characterized by means of SEM-EDS and scanning Kelvin probe force microscopy（SKPFM）. The experimental results indicate that there are two different intermetallics：A1-Mn-Fe and Mg2Si. Both intermetallics exhibite the negative volta potential relative to the matrix indicating an anodic behaviour. Hereby, they are easy to be dissolved and corroded under the erosive environment, and there become the corrosion initiation sites. The A1-Mn-Fe intermetallics show stronger anodic behaviour than those of Mg2Si intermetalics. It means that A1-Mn-Fe intermetalics are easier to be corroded.

Initial micro-galvanic corrosion behavior between Mg_(2)Ca and α-Mg via quasi-in situ SEM approach and first-principles calculation

The initial micro-galvanic corrosion behavior of Mg-30wt%Ca alloy only containing Mg_(2)Ca andα-Mg was studied by immersion testing in a 0.9%Na Cl solution at 37°C.The quasi-in situ SEM and TEM results show that Mg_(2)Ca corroded easier thanα-Mg,indicating that Mg_(2)Ca acted as an anode.The work function(Φ)for Mg_(2)Ca calculated by first-principles is significantly lower compared to that forα-Mg.The Volta potential measured by a scanning Kelvin probe force microscope reveals that the Mg_(2)Ca had a relatively low Volta potential(ψ)value.The lowerΦandψvalues for Mg_(2)Ca indicate a lower electrochemical nobility,which is consistent with the experimental phenomenon.

Role of trace additions of Ca and Sn in improving the corrosion resistance of Mg-3Al-1Zn alloy

The limited wide applicability of commercial Mg alloys is mainly attributed to the poor corrosion resistance.Addition of alloying elements is the simplest and effective method to improve the corrosion properties.Based on the low-cost alloy composition design,the corro-sion behavior of commercial Mg-3Al-1Zn(AZ31)alloy bearing minor Ca or Sn element was characterized by scanning Kelvin probe force microscopy,hydrogen evolution,electrochemical measurements,and corrosion morphology analysis.Results revealed that the potential differ-ence of Al_(2)Ca/α-Mg and Mg_(2)Sn/α-Mg was(230±19)mV and(80±6)mV,respectively,much lower than that of Al_(8)Mn_(5)/α-Mg(430±31)mV in AZ31 alloy,which illustrated that AZ31-0.2Sn alloy performed the best corrosion resistance,followed by AZ31-0.2Ca,while AZ31 al-loy exhibited the worst corrosion resistance.Moreover,Sn dissolved into matrix obviously increased the potential ofα-Mg and participated in the formation of dense SnO_(2) film at the interface of matrix,while Ca element was enriched in the corrosion product layer,resulting in the cor-rosion product layer of AZ31-0.2Ca/Sn alloys more compact,stable,and protective than AZ31 alloy.Therefore,AZ31 alloy bearing 0.2wt%Ca or Sn element exhibited excellent balanced properties,which is potential to be applied in commercial more comprehensively.

Improving corrosion resistance of Zn-5Al(wt%)alloy by microalloying with samarium

The role of the rare earth element Sm in as-cast Zn-5AI alloy was studied in this work.A three times higher improvement than the control group on corrosion resistance was found with rare earth Sm adding(0.15 wt%).By using an electron prove micro analyzer(EPMA),focused ion beam(FIB)and scanning Kelvin probe force microscopy(SKPFM)techniques,two main mechanisms of the premium performance of the Sm adding were revealed.One was that the non-uniform nucleation and component undercooling induced by Sm adding,reduced theα-AI layer spacing thus improved the covering efficiency of the Al_(2)O_(3)film.The other was that the dissolved Sm in the Zn/Al eutectic structure modulated the electron work function thus induced the attenuation of Volta potential discrepancy.The experimental results show that when the addition of Sm is 0.15 wt%,the minimum Volta potential difference betweenα-AI andη-Zn phases is achieved,and excessive or deficient Sm addition will increase the Volta potential difference.

Role of Microalloyed Y and Gd in Improving the Corrosion Resistance of Rolled Mg-3Al-1Zn Alloy

The corrosion performances of rolled AZ31 alloy with addition of Y and Gd were comparatively investigated. The corrosion rates of AZ31 alloy modified with Y and Gd were 3.3 and 3.7 mm/y immersing for 24 h in 3.5 wt% NaCl solution, respectively, which were much lower than that of AZ31 alloy(23.6 mm/y). The remarkable improvement in corrosion performance by adding Y or Gd was ascribed to preferentially form less noble Al_(2)Y or Al_(6)GdMn_(6) and more protective corrosion product layer, resulting in the reduction in H_(2) evolution rate and the enhancement of passivity.