Intergranular Corrosion and Microstructural Evolution in a Newly Designed Al-6Mg Alloy.

Kweon-Hoon Choi,Seong-Ho Ha,Young-Ok Yoon,Seung-Yoon Yang,Hyun-Kyu Lim,Da-Bin Lee,Bong-Hwan Kim,Nam-Seok Kim,Shae-Kwang Kim

doi:10.3390/ma14123314

Abstract

In this work, the microstructure and corrosion behavior of a novel Al-6Mg alloy were investigated. The alloy was prepared by casting from pure Al and Mg+Al2Ca master alloy. The ingots were homogenized at 420 °C for 8 h, hot-extruded and cold-rolled with 20% reduction (CR20 alloy) and 50% reduction (CR50 alloy). The CR50 alloy exhibited a higher value of intergranular misorientation due to a higher cold rolling reduction ratio. The average grain sizes were 19 ± 7 μm and 17 ± 9 μm for the CR20 and CR50 alloys, respectively. An intergranular corrosion (IGC) behavior was investigated after sensitization by a nitric acid mass-loss test (ASTM G67). The mass losses of both the CR20 and CR50 alloys were similar at early periods of sensitization, however, the CR20 alloy became more susceptible to IGC as the sensitization time increased. Grain size and β phase precipitation were two critical factors influencing the IGC behavior of this alloy system.

Highlights

The 5xxx series Al-Mg alloys are widely used materials in the automotive industry due to their high strength-to-weight ratios, weldability, and good corrosion resistance [1,2,3].Strength and ductility can be improved by adding solute Mg to the alloys because of the solid solution strengthening mechanism [4,5]
The results reveal that the CR20 alloy has more equiaxed grains compared to the CR50 alloy
It was revealed that the grain size and the continuity of β precipitation play an important role in intergranular corrosion (IGC)

Summary

Introduction

The 5xxx series Al-Mg alloys are widely used materials in the automotive industry due to their high strength-to-weight ratios, weldability, and good corrosion resistance [1,2,3]. Strength and ductility can be improved by adding solute Mg to the alloys because of the solid solution strengthening mechanism [4,5]. The rapid oxidation of magnesium alloys can be suppressed by additions of Ca [7]. With this background, a new alloying strategy has been developed. The strategy uses an Mg + Al2 Ca master alloy instead of pure Mg during casting.

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