Evaluation HPDC Lubricant Spraying for Improved Cooling and Die Protection

This study tries to find out a better cooling and temperature homogenization as well as better die protection on high-pressure die-casting (HPDC) spray lubrication. Test procedures have been set up to study the Leidenfrost point (LFP), contact angle (CA), film thickness and protection from die soldering of lubricants typically applied into the die surfaces during HPDC process. Five different lubricants have been studied as well as the influence in different controllable process parameters (type of die material, oxidation of the surface, temperature, roughness, droplet diameter, water hardness and lubricant concentration). The increase of the LFP, avoiding film boiling regime, and a reduced CA, improve the cooling and film ability of die surface during spraying. The best chemistry exhibits high LFP, shows an increased thickness of the formed film and is more effective preventing the sticking of the aluminum part to the die surface. Thermogravimetric analysis shows better thermal properties for lubricants with anti-sticking performance. The study performed and the test protocols set up result in a better insight of the involved phenomena and allow selecting the most favorable operating window for HPDC lubrication

Repeatability of tensile properties in high pressure die-castings of an Al-Mg-Si-Mn alloy

© 2015 The Korean Institute of Metals and Materials and Springer Science+Business Media Dordrecht High pressure die-castings of an Al-Mg-Si-Mn alloy have been assessed in terms of the repeatability of the mechanical properties including yield strength, ultimate tensile strength and elongation by the normal standard deviations method and by the Weibull statistical model with three parameters. It was found that the round samples had the maximum Weibull modulus, indicating the best repeatability. The machined samples exhibited the second best of Weibull modulus. Among the square samples, the 2 mm and 5 mm thick samples had the lowest and the highest Weibull modulus respectively, indicating that the repeatability for the castings was influenced by the wall thickness. The microstructural uniformity and porosity levels are critical factors in determining the repeatability of the high pressure die-castings. A less segregation in the microstructure could uniform the stress distribution in the die-castings and a less porosity in the casting could reduce the sources for brittle fracture. These improved the repeatability in casting production.The authors acknowledge the Engineering and Physical Sciences Research Council (EPSRC), Technology Strategy Board (TSB) and Jaguar Land Rover (JLR) in United Kingdom for financial support

Combined deformation and solidification-driven porosity formation in aluminum alloys

In die-casting processes, the high cooling rates and pressures affect the alloy solidification and deformation behavior, and thereby impact the final mechanical properties of cast components. In this study, isothermal semi-solid compression and subsequent cooling of aluminum die-cast alloy specimens were characterized using fast synchrotron tomography. This enabled the investigation and quantification of gas and shrinkage porosity evolution during deformation and solidification. The analysis of the 4D images (3D plus time) revealed two distinct mechanisms by which porosity formed; (i) deformation-induced growth due to the enrichment of local hydrogen content by the advective hydrogen transport, as well as a pressure drop in the dilatant shear bands, and (ii) diffusion-controlled growth during the solidification. The rates of pore growth were quantified throughout the process, and a Gaussian distribution function was found to represent the variation in the pore growth rate in both regimes. Using a one-dimensional diffusion model for hydrogen pore growth, the hydrogen flux required for driving pore growth during these regimes was estimated, providing a new insight into the role of advective transport associated with the deformation in the mushy region

Analisi sperimentale della saldatura a fascio elettronico di una lega d'alluminio altoresistenziale

Nella presente memoria vengono esposti i principali risultati ottenuti in un lavoro sperimentale avente lo scopo di caratterizzare la saldabilt\ue0 al fascio elettronico di una lega di alluminio altoresistenziale. Nella fase preliminare dello studio, \ue8 stata effettuata una accurata caratterizzazione del metallo base mediante le usuali tecniche di indagine metallografica e prove di microdurezza. La saldatura vera e propria \ue8 stata effettuata dopo alcune prove di penetrazione, volte a determinare i parametri di processo e le modalit\ue0 di esecuzione ottimali. Le indagini al microscopio ottico del cordone hanno evidenziato una eccellente saldabilit\ue0 con la quasi totale mancanza di porosit\ue0 o difetti microstrutturali. Le prove di microdurezza hanno inoltre messo in evidenza la presenza di una zona termicamente alterata di ridotte dimensioni e di una zona fusa con un elevato aspetto di figura, grazie al notevole effetto di direzionalit\ue0 dato dal fascio elettronico

Caratterizzazione degli stampi in lega Al

Le caratteristiche delle leghe di alluminio possono costituire un vantaggio nella realizzazione di uno stampo oppure nella sua successiva utilizzazione. In questo articolo vengono illustrate alcune tecnologie d'avanguardia per 10 studio del comportamento delle legbe di alluminio, con particolare riguardo aIle leghe quaternarie (Zn-AI-Cu-Mg)