UCTEA Chamber of Metallurgical & Materials Engineers Proceedings Book

856 IMMC 2016 | 18th International Metallurgy & Materials Congress

Corrosion Behavior of V Modifi ed A360 Alloy Eda Ergün Songül, Derya Dışpınar, Gökhan Orhan İstanbul University - Türkiye

Abstract Al-Si alloys are preferred choice of material for high pressure die casting applications. This is due to the physical properties of silicon. Silicon increases fluidity, decreases solidification shrinkage and improves mechanical properties. In addition, corrosion resistance is increased with increased Si content. Microstructure plays a significant role in determining the several properties of aluminium alloys. Therefore, in this work, the effect of addition of V on the corrosion behaviour of A360 alloy was investigated. Tafel curves were carried out on the cast samples with various V additions. It was found that up to 0.02 wt% V, corrosion resistance was improved however higher additions had decreased corrosion behaviour. 1. Introduction McCartney [1] claimed that vanadium was a more effective grain refiner than titanium in his study. Increased V content in aluminum alloy containing high Cu and Mg was provided to form Al-V and Al-Cr intermetallics which were improved the hardness of the alloy [2]. As a result of V addition to Al-Si alloys, has been achieved to increasing 45% in yield and 20% in tensile strength [3]. According to another claim of Casari, Al-7Si alloy had become more brittle by V addition [4]. In Di Giovani doctoral thesis has been characterized mechanical properties of V added Al-Si alloys [5]. In this paper, electrochemical potentiodynamic test was conducted to understand the effect of V addition on the polarization behaviours of A360 alloy. 2. Experimental Procedure The composition of A360 alloy used in the tests is given in Table 1. Resistance furnace was used to melt the charges at 710oC. After degassing, the samples were cast into a mould design where cylindrical and rectangular test bars were produced by 160 ton HPDC machine.

Table 1.Chemical analysis of A360 alloy (wt%) Fe Si Cu Mn Mg Sr

0,48 9,42 0,06 0,44 0,39 0,02

Initially, Al-10% Sr master alloy was added in order to obtain 200 ppm Sr in the alloy. Then, Al-10%V master alloy was used to produce samples with 0.01, 0.02, 0.04 and 0.08 wt % V in the alloy. Electrochemical behaviour of A360 specimens were tested in 3.5 wt.% NaCl solution at room temperature (23±10C) by means of potentiodynamic polarization using Gamry Instrument Model 600 Electrochemical Workstation. 3. Results and Discussion The Tafel curves of A360, A360 alloy with Sr and V modification were given in Figure 1. While the corrosion current density (icor) of A360 alloy with Sr modification was increased, the corrosion current density (icor) of A360 alloy with Sr+V was decreased.

Figure 1. Potentiodynamic polarization curves of A360,

A360 alloy with Sr and V modification When V addition ratios on the corrosion behaviour of A360 alloy were to be investigated, it can be seen from Figure 2 that increase from 0.01 to 0.02 wt% V addition significantly improved corrosion resistance. However, further increase in V addition (0.04 and 0.08 wt%) decreased the corrosion properties (Figure 3).

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Figure 2. Potentiodynamic polarization curves of Sr modified A360 alloy with 0.01 and 0.02 wt% Vaddition

Figure 3. Potentiodynamic polarization curves of Sr modified A360 alloy with 0.04 and 0.08 wt% V addition

The optical microscope images of A360 alloy,A360 alloy with Sr and V modification were given in Figure 4,5 and 6.

Figure 4. Microstructure of A360

Figure 5. Microstructure of Sr modified A360

Figure 6. Microstructure of Sr+V modified A360

When Figure 4-6 is compared, it can be seen that eutectic phase ratio is high in A360; it increased when Sr is added to alloy and decreases again when V is added.

4. Conclusion

• When Sr is added to A360, corrosion resistance decreased.

• When V is added together with Sr to A360, corrosion resistance was improved when 0.01 and 0.02 wt% V was added but it was decreased with increased V additions.

• Optimum corrosion resistance was found when 200 ppm Sr and 0.02wt% V was added to A360.

• Corrosion resistance was in good agreement with the eutectic phase ratio. When volumetric ratio of dendrites were increased, corrosion resistance was decreased.

UCTEA Chamber of Metallurgical & Materials Engineers Proceedings Book

858 IMMC 2016 | 18th International Metallurgy & Materials Congress

Acknowledgment The authors would like to acknowledge the support of AlCast Metal San. Tic. Ltd. ti. References [1] McCartney, D. G. (1989). Grain refining of aluminium and its alloys using inoculants. International Materials Reviews, 34(1), 247-260. [2] Beerntsen, D. J. (1977). Effect of vanadium and zirconium on the formation of CrAI 7 primary crystals in 7075 aluminum alloy. Metallurgical and Materials Transactions B, 8(3), 687-688. [3] Casari, D., Ludwig, T. H., Merlin, M., Arnberg, L., & Garagnani, G. L. (2014). The effect of Ni and V trace elements on the mechanical properties of A356 aluminium foundry alloy in as-cast and T6 heat treated conditions. Materials Science and Engineering: A, 610, 414-426. [4]Casari, D., Ludwig, T. H., Merlin, M., Arnberg, L., & Garagnani, G. L. (2015). Impact Behavior of A356 Foundry Alloys in the Presence of Trace Elements Ni and V. Journal of Materials Engineering and Performance, 24(2), 894-908. [5]Di Giovanni, M. T. (2014). The Influence of Ni and V Trace Elements on the High Temperature Tensile Properties of A356 Aluminium Foundry Alloy.