Browsing by Author "Bobzin, Kirsten"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item Investigation of HVOF spraying on magnesium alloys(2006-12-04) Parco, Maria; Zhao, Lidong; Zwick, Jochen; Bobzin, Kirsten; Lugscheider, Erich; EXTREMATMagnesium alloys are promising alternatives to other lightweight alloys such as aluminum alloys due to their high specific strength and stiffness. However, the use of magnesium alloys is limited by their poor wear behaviour and corrosion performance. Recent studies have shown an enormous potential of thermal spray techniques for the surface modification of Mg alloys. The high particle velocities and moderate temperatures achieved by the High Velocity Oxy-Fuel (HVOF) flame spray process lead to very dense coatings with outstanding wear behaviour and superior bond strengths in comparison to other thermal spray processes. In this study, two Mg alloys AZ91 and AE42 were coated using the HVOF spray process. The substrates were compared in terms of the measured bond strength and the observed adhesion mechanisms of the coating. Furthermore, the coatings were characterized concerning their corrosion performance on AZ91 substrates. It was found that dense WC-Co coatings could be applied on Mg alloy substrates using the HVOF spray process. The high kinetic energy of the WC-Co particles led to a "self roughening" effect on the substrate, enabling the deposition on polished Mg alloy substrates. The coatings showed a very good adhesion to the substrates. The corrosion tests showed that the unsealed WC-Co coatings could not improve the corrosion performance of Mg alloys. In contrast, the duplex coating system with an Al bond coat improved significantly the corrosion resistance of Mg alloys. The sealed coatings showed a very good corrosion behaviour.Item Investigation of particle flattening behaviour and bonding mechanisms of APS sprayed coatings on magnesium alloys(2007-02-04) Parco, Maria; Zhao, Lidong; Zwick, Jochen; Bobzin, Kirsten; Lugscheider, Erich; EXTREMATMagnesium alloys are promising alternatives to other lightweight materials due to their high specific strength and stiffness. However, the use of magnesium alloys is limited by their poor wear behaviour and low corrosion resistance for many industrial applications. The thermal spray technology offers a wide range of possibilities to improve the surface properties of Mg-based components. In this study, three different coating materials, namely Al, NiAl5 and Al2O3, were applied on AZ91 and AE42 substrates using the atmospheric plasma spray technology. The investigation was focused on the bonding strength of the coatings and the related bonding mechanisms. For a better understanding of the bonding mechanisms, the flattening behaviour of the spray particles was investigated in correlation with the substrate pre-heating temperature. It was found that NiAl5-particles could well melt the substrate at the surface and deformed it locally; Al-particles did the same but to a lower extent. The dominating bonding mechanism for NiAl5-coatings could be attributed to a metallurgical bonding. For Al-coatings, this mechanism played a more important role once the substrate pre-heating temperature was increased. Al2O3 particles in contrast, were less able to deform the substrate in spite of their higher thermal load and the mechanical anchoring remained the main bonding mechanism. The thermo physical properties of the Mg substrate showed also to have an influence on the adhesion of the coatings.