Precipitation hardening in Mg-RE alloys is an effective strengthening mechanism to achieve high strength at moderate ductility. WE43 has already shown an acceptable biological response. Two Mg-Y-Nd-Gd-Dy alloys are used in this study. Even the changes in chemical composition of the two alloys are rather small, hardness, strength and ductility differ for the three material conditions: extruded, solution heat treated and precipitation hardened. Improved strength by precipitation hardening affects corrosion by finely dispersed particles, being often more noble than the matrix. Biodegradable implant material should show a certain corrosion rate, but should be free of pitting. Deep pits act as notches, which cause higher mechanical stress concentration. Solution heat treatment causes grain growth and strength loss. A rather short ageing response is found. Grain growth during ageing is not significant. Corrosion has been evaluated with potentiodynamic polarization and immersion tests in Ringer solution and the corrosion behaviour is described by corrosion rate, shape and amount of deep pits and pitting factor. These values depend strongly on the chemical composition, heat treatment and the test method itself.