Mechanical and Corrosion Properties of Two Precipitation-Hardened Mg-Y-Nd-Gd-Dy Alloys with Small Changes in Chemical Composition

Abstract

Nd alloys is based on finely dispersed particles an effective strengthening mechanism to achieve high strength at moderate ductility. However, these particles often affect corrosion by being more noble than the matrix. Biodegradable implant materials should show a corrosion rate fit to its application but should be free of pitting corrosion. Especially deep and narrow pits act as notches and cause increased mechanical stress leading into early failure. WE43 has already shown to have an acceptable biological response. In this study two Mg-Y-Nd-Gd-Dy alloys, WE32 and WE33, in extruded, solution and precipitation heat-treated conditions have been investigated. The difference in alloy composition is not very high. Solution heat treatment causes grain growth and strength loss. The ageing response to peak hardness depends on the temperature. A rather short ageing response was observed for 250 °C and for 200 °C highest hardness has been found at longer ageing time, but higher hardness compared to 250 °C. Grain growth during ageing is not significant. The higher alloyed alloy WE33 shows better mechanical strength, but less ductility. Corrosion was evaluated with immersion and potentiodynamic polarization in Ringer Acetate solution. The corrosion rate strongly depends on the alloy and heat treatment condition as well as on the test method. The highest corrosion rate is observed in the T4 condition. The peak aged alloy shows the lowest corrosion rate, but non-uniform corrosion-in this evaluated by the pitting factor.

Archives of Metallurgy and Materials

“…Because with a lower corrosion rate as a result of passivation (see Fig. 8) the pitting factor increases when the oxide layer is obviously not dense enough, which agrees with the immersion tests [54]. However, pitting factor is the lowest in the as-cast Q5 alloy.…”

Influence of Solution Heat Treatment on the Microstructure, Hardness and Stress Corrosion Behavior of Extruded Resoloy®

“…WE43 is a high-strength alloy with an acceptable biological response. [6][7][8] The alloying, manufacturing route and post-heat treatment influence the mechanical and corrosion properties of this material. Nd, for example, is known to form stable intermetallic phases at grain boundaries, as Nd has a low solid solubility in Mg and is therefore added to provide precipitation strengthening.…”

Deformation Behavior of β Phase in a WE54 Magnesium Alloy

“…Li et al [ 30 ] reported that the yielding plateau at the initial stage of plastic deformation is mainly ascribed to the activation of, and rapid increase in, basal dislocations. Figure 3 b presents the mechanical properties of different extruded WE alloys [ 14 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 ], suggesting the overall superior properties of the alloy in this work.…”

“… Mechanical properties of the extruded alloy at room temperature. ( a ) Engineering stress–strain curve; ( b ) comparison of the elongation and yield stress of different extruded WE alloys [ 14 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 ]. …”