Papers by Author: Massimiliano Bestetti

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.

Abstract: In this paper a protection process against corrosion and wear for AM60B magnesium alloys, by multilayer approach, is related. The coating consists of a porous oxide layer, obtained in micro-arc anodizing regime, and two or three layers deposited by sol-gel technique. The anodic oxidation pre-treatment improves the adhesion of the sol-gel layers, which are responsible for the sealing of the anodic oxide pores and for the corrosion protection effect. In addition the multilayer system significantly improves AM60B alloy wear resistance. Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) were employed to assess morphology and crystallographic structure. Electrochemical polarization and wear tests were performed in order to evaluate the corrosion resistance behaviour and the wear resistance of the coated magnesium alloys.

Abstract: Oxide films have been produced on the AM60B magnesium alloy using micro-arc oxidation process in an environmentally friendly alkaline solution with and without addition of titania nanoparticles. The surface morphology and cross-section of anodized samples were analyzed by Scanning Electron Microscopy (SEM) coupled with EDS and the phase composition was investigated by X-ray Diffraction (XRD). Hardness tests were performed by means of a micro-hardness tester and the corrosion resistance was evaluated in 3.5% NaCl solution using potentiodynamic polarization tests. Addition of titania nanoparticles doesn’t affect corrosion resistance significantly, but the oxide films produced in titania-containing solution are denser, thicker and have more uniform morphology. In the oxides produced at 130V-140V in presence of titania (4g dm-3) a spinel (MgAl2O4) was observed. Spinel phase increases the hardness up to 550 HV (10mN, 10 s). The addition of titania nanoparticles in the solution could be an interesting way to synthesize hard coatings on magnesium alloy AM60B by micro-arc oxidation in a short process time (10 minutes).