Analysis of different inhibitors for magnesium investment casting

Investment casting of magnesium is a well suited process for the production of aeronautic and automotive components. But still, this process has not been properly developed. One reason for that are the reactions between the Mg melt and the ceramics of the mould that produce a non-desired oxide layer on the part surface. These reactions can be inhibited by the use of silica-free slurries with a higher stability than conventional ones. Another way is using inhibitors, chemical compounds based in fluorides that react with the melt, creating a protective surface layer in the casting. With the aim of developing a reaction-free process, alumina moulds with a stepped geometry have been constructed. These provide different interface conditions. Conventional SF6, non-conventional KBF4 and NaBF4, and environmentally friendly FK inhibitors have been tested on. As a result, KBF4 has been identified as the most suitable inhibitor for magnesium investment casting. Furthermore, the analysis of the cooling curve of different interfaces has provided essential information about the reaction mechanism of the inhibitors

Influence of Surface Finish and Porosity on the Fatigue behaviour of A356 Aluminium Casting Alloy

In casting parts, due to the manufacturing process, the presence of defects such as porosity, inclusions and oxide films is unavoidable. All these irregularities have a negative effect on the component performance. Several works have demonstrated that, among them, porosity is especially detrimental to the fatigue properties. As most fatigue failures nucleate at the surface of a material, casting defects at or near the surface and surface roughness become an extremely important factor in determining the fatigue strength of cast components.Very little research has been conducted into the influence of both surface quality and porosity on the fatigue behaviour of aluminium castings parts. In the present work, the effects of two different surface qualities (machined and as-cast) on fatigue behaviour of an A356 casting alloy were studied. The S-N curves obtained showed that the cast surface had higher fatigue strength than the machined one. The failure in cast specimens initiated predominantly from valleys of the rough surface near pores or inclusions. On the other hand, in machined surfaces, the cracks initiated directly from surface pores. Thus, the improvement in fatigue life was attributed to a longer crack “initiation” period

Press hardening of alternative materials: conventional high- strength steels

he increase in strength of new high strength steels(HHS) and advanced high strength steels (AHHS) has led toforming issues, such as high springback, low formability, increase of forming forces and tool wear. These problems increase thecosts of manufacturing and maintainingstamping tools in the automotive industry. The aim of this research was to analyse the advantages of applyingthe press-hardening process toconventional HSS and AHSS steel to increase their formability and therefore reduce thenumber of forming steps and productioncosts. With this aimin mind, the press-hardening process was used to manufacturean industrialcomponent using four different automotive steelgrades: dual phase (DP),complex phase (CP), transformation-induced plasticity (TRIP) and martensitic (MS) grade.Springback measurements werecarried out, together with ananalysis of the obtained final mechanical properties and microstructures. The results showed that the formability of all thematerials increased. The mechanical properties of theCP800and TRIP700 materials were maintained or even improved, whereas those of the MS1200 and HCT980Xmaterials were significantly reduced. Weconclude thatpress hardening is a suitable manufacturing processforCP800 and TRIP700components

Influence of Surface Finish and Porosity on the Fatigue behaviour of A356 Aluminium Casting Alloy

In casting parts, due to the manufacturing process, the presence of defects such as porosity, inclusions and oxide films is unavoidable. All these irregularities have a negative effect on the component performance. Several works have demonstrated that, among them, porosity is especially detrimental to the fatigue properties. As most fatigue failures nucleate at the surface of a material, casting defects at or near the surface and surface roughness become an extremely important factor in determining the fatigue strength of cast components. Very little research has been conducted into the influence of both surface quality and porosity on the fatigue behaviour of aluminium castings parts. In the present work, the effects of two different surface qualities (machined and as-cast) on fatigue behaviour of an A356 casting alloy were studied. The S-N curves obtained showed that the cast surface had higher fatigue strength than the machined one. The failure in cast specimens initiated predominantly from valleys of the rough surface near pores or inclusions. On the other hand, in machined surfaces, the cracks initiated directly from surface pores. Thus, the improvement in fatigue life was attributed to a longer crack “initiation” period