Abstract
Magnesium raises more and more interest in the car industry in the perspective to reach future CO2 emission requirements. For current inner applications, like instrument panels or seat frame structures, ductility requirements tend to increase. Magnesium is now also considered in the body structure area. For these reasons, Brabant has launched an innovation programme to improve the elongation of magnesium die cast parts.
For High Pressure Die Casting large structural parts, properties can be described as per a composite structure. The skin is homogeneous all over the part showing a high ductility. The core structure has a high elongation close to the gate; however, as the distance from the gate increases, ductility tends to decrease and scatter increases. The definition of a conservative design elongation value goes through massive testing (locations and load cases). In this perspective, it has been chosen to focus on mechanisms that could either improve the average ductility or reduce the scatter. The three first tested factors are the influence of the key process parameters (through a design of experiment), the influence of “supporting techniques” to the die casting process and finally the use of grain refiners developed by the University of Brunel to minimize the pre-solidification mechanisms that can take place. All investigation is carried out on component tests and on real production conditions.
Ductility performance is mostly driven by the scatter as demonstrated by the design of experiment on process parameters. The melt temperature and the lube ratio are the two factors driving the scatter in elongation values. Trials with “supporting techniques” have proven a high efficiency to reduce scatter in elongation values, impacting average results. The grain refiners improve elongation; they have no impact on scatter.
This study applies to High Pressure Die Casting of Magnesium AM alloys. For large cast components having a size comparable to an instrument panel, a seat frame structure or a front end carrier. For these components, the wall stoke usually ranges from 2 to 5 mm with a nominal wall thickness of 2,6 mm.
The analysis of the scatter in performance offers a different reading of the impact of any improvement that can be made to the High Pressure Die Casting process of Magnesium AM alloys. If the effect of some factors would hardly be noticeable on the average performance, the analysis of the “1 part per million performances” gives more interesting information when designing for robustness. The impact of the tested location is also important to get the full understanding of the process.
Through a statistical analysis of the tested deflections for failure and a finite element reverse engineering analysis on the corresponding elongation to failure, it has been assessed that a 10% elongation value could be used for design, if all improvements were implemented into the process. More experience on other parts and other load cases is required prior to freeze such a design value; however, initial results are encouraging. Other factors will be tested to improve further the ductility; then riveting trials will have to be performed as body parts applications are considered.
Brabant Alucast was founded in 2007 and consists of 6 highly automated operating companies in Europe and Brasil. The group combines a long history of casting and machining with the development of new technologies. As a leading specialist in the design, development and production of high-pressure die cast aluminium and magnesium components for the automotive industry, Brabant Alucast is among the best in the European industry ranked by quality and annual turnover. The company supplies components to practically all the major automotive brands worldwide. Brabant Alucast has a unique understanding of all aspects of high-pressure diecasting, as is shown by Exactfit Casting™ and Vacural® Casting, two technologies developed in-house by our R&D team, which achieve exceptional results in the die casting process. Brabant Alucast is also specialized in complex CNC machining and assembly, using the most advanced computer-controlled machines available.
KEYWORDS – High pressure die casting, Magnesium alloys, AM50A, Ductility, Scatter