Role of post-heat treatment on hardness, bending strength and corrosion of Mg4Gd wire compared to pure Mg wire


Mg4Gd wires in as-drawn condition show strong local corrosion, which greatly reduces the remaining tensile and bending strength. The initial strength and ductility is rather high due to the fine grained microstructure as a result of recrystallization during the complex forming procedures. Small grains and intermetallics increase strength. However, intermetallics have a pronounced influence on corrosion. Pitting can be either caused by microgalvanic corrosion or by forming passive layers (here not stable enough). Mechanical and corrosion properties are studied using microhardness, tensile- and bending tests, corrosion itself and stress corrosion (Ringer solution, 37°C) in comparison with as-drawn and T4 material. T4 relieves inner stress and leads to less anodiccathodic coupling due to dissolved intermetallics. Hardness increase caused by tensile and compressive stresses during 3-point-bending has been investigated as well as its influence on corrosion. Tensile stresses cause open pores within the oxide layer and accelerate corrosion. Mechanical and corrosive properties are compared to pure Mg wires. Post-heat treatment tailors properties between higher strength, but higher corrosion rate (as-drawn), and less strength, but lower corrosion rate (T4) and influences the life time in stress corrosion. Stress corrosion cracking is either driven by continuous cracking resulting in dissolution within crack front or by cleavage fracture leading to discontinuous crack propagation. An improvement of corrosion behavior by post-heat treatment is seen.
QR Code: Link to publication