Corrosion Behaviour of High Pressure Die-Cast and Semi-Solid Cast AZ91, AM60 and AM50 Alloys

Abstract:

A comparison of corrosion resistance of die-cast and semi-solid cast AZ91, AM60 and AM50 magnesium alloys was performed in different corrosive media by measurement of the open circuit potential, potentiodynamic scans and weight loss tests. Before testing, a heat treatment was carried out onto semi-solid cast alloys. Electrochemical measurements have shown that the semi-solid cast alloys have a different corrosion rate compared to the die-cast ones. The results could be correlated to the different microstructures of the samples produced by the different processes.

• Periodical: Solid State Phenomena (Volumes 192-193)
• Pages: 231-237
• DOI: https://doi.org/10.4028/www.scientific.net/SSP.192-193.231
• Online since: October 2012
• Authors: Simone Umberto Mariani, Anna da Forno, Massimiliano Bestetti
• Keywords: Corrosion Resistance, Die-Cast, Magnesium Alloy, Semi-Solid Cast

References

[7] days ΔWeight Weight loss Corrosion rate3 (cm2 ) (g) (g) (g) (mg day-1 dm-2 ) (μA cm-2 ) AM60 DIE-CASTING

[4] 6.1329 6.1288 0.0041 14.6 13.5 AM60 R-HPDC (without heat treatment) 4 7.3081 7.3048 0.0033 11.8 10.8 AM60 R-HPDC (with heat treatment) 2 3.1766 3.1749 0.0017 12.1 11.2           AZ91 DIE-CASTING

[4] 5.6295 5.6277 0.0018 6.4 5.9 AZ91 R-HPDC (without heat treatment) 4 6.1064 6.1049 0.0015 5.4 4.9 AZ91 R-HPDC (with heat treatment) 2 4.0331 4.0325 0.0006 4.3 3.9           AM50 DIE-CASTING

[4] 0.814 0.8116 0.0024 8.6 7.9 AM50 R-HPDC (without heat treatment) 4 6.4776 6.4738 0.0036 13.6 12.5 AM50 R-HPDC (with heat treatment) 2 3.5172 3.5166 0.0006 4.3 3.9 As shown in Table 1, die-cast AM60 has higher corrosion rates than that of die-cast AM50 and AZ91. In the case of AM50 samples the highest corrosion rate is that of R-HPDC samples not thermally treated. For all the samples the corrosion rates of heat treated R-HPDC are lower than those of untreated R-HPDC and die-cast alloys. In comparison with die-cast samples the corrosion rates of the alloys R-HPDC with heat treatment are significantly lower. The corrosion current densities obtained from the weight loss measurements are greater with respect to those derived from dynamic polarization measurements, even though they are in good agreement for what concerns the ranking. In particular, for the three types of AM60 alloy samples the calculated corrosion current densities by weight loss have proved to be higher than those of the other alloys and among them quite similar. Summary In the light of the achieved results, we can state that the electrochemical tests have shown better corrosion resistance for heat treated R-HPDC AM50 alloy in comparison with untreated R-HPDC AM50 and die-cast AM50. For AZ91 alloy the results are controversial and further investigations are necessary, while for AM60 the die-cast corrosion resistance measured by electrochemical tests is higher than that of R-HPDC alloys. On the contrary, weight loss measurements show a better corrosion resistance of the heat treated R-HPDC alloys in comparison with the die-cast and the untreated R-HPDC. References