A more resilient, tougher alloy widely used in the automotive industry
The light, aluminium-silicon alloy of great interest for industry (the auto industry, in particular), produced by means of a novel process starting from a semi-solid state, displays better mechanical properties (such as tensile strength, resilience and toughness) and better corrosion resistance than that produced using the usual high-pressure processes. This has been demonstrated by the engineer Leire Solaberrieta-Ostolaza of the NUP/UPNA-Public University of Navarre.
Solaberrieta's research, conducted in the research group of the Materials Area of the NUP/UPNA's Department of Mechanical, Energy and Materials Engineering, addresses the interest of industry (in particular the automotive sector) in coming up with metal alloys that are lighter than the ones currently used and which retain their mechanical properties and corrosion resistance.
An alloy extensively used in cars
With this aim in mind, the researcher selected the aluminium-silicon alloy (AA380), extensively used in the automotive industry, and studied the effect of casting and die manufacturing processes on its mechanical properties and corrosion resistance. "Samples were obtained by means of two different forming processes: the one most commonly used by the industry over the last decade, known as High Pressure Die Casting or HPDC, in which the metals are injected into the mould in a liquid state; and one of the new emerging processes that are being deployed in the most advanced industries in the sector, the so-called Semi Solid Rheocasting or SSR, in which semi-solid metals are injected," explained Solabarrieta.
After that, she used a range of techniques and analyses to study and compare the microstructure of the materials obtained. "The main difference between the two types of material is the grain size, bigger in the case of the samples obtained by means of SSR," said the new PhD holder. "This improves the mechanical properties of the alloys obtained through this process: toughness, elongation and tensile strength are increased, and the absorption of impact energy remains similar".
The corrosion resistance of the materials was analysed by using industrial characterisation tests in line with the standards as well as advanced electrochemical techniques. "The alloy studied displays poor resistance to corrosion processes in both processes due to the high copper content. Yet, in the case of SSR, the results were slightly better," she pointed out.
Finally, the researcher analysed two techniques designed to protect these alloys: polymer coatings and anodizing or increasing the thickness of the natural layer of oxide on the surface of the parts. "The die-cast material turned out to be more difficult to anodize than the material produced by forging, owing to its silicon content. However, the samples obtained through SSR die casting displayed a lesser quantity of silicon and thanks to that the anodized layer produced is bigger than in the samples in the other process," she concluded.
Provided by Elhuyar Fundazioa