Papers by Author: Zigor Azpilgain

Abstract: Aluminium alloys are more and more important for the automotive industry due to their high strength to weight ratio and their elevated ductility; they are used for many different parts in automobiles as exterior panels, structural parts, brake housings and others. However, their formability at room temperature is limited. This inconvenient can be improved by increasing the forming temperature of the part. That lack of formability has lead to this research project dealing with the tensile behaviour of aluminium alloys sheets, at different conditions of temperature and strain rate. The analyzed material has been 6082 aluminium alloy, under two different heat treatment conditions (O and T6). Material testing has been carried out in a temperature range between room temperature and 250°C, and a strain rate range between 0.001s-1 and 0.1s-1. Testing samples have been obtained from laminated sheet of 1.5mm thickness. This article shows that the alloy under T6 condition has a reduced formability, even in warm conditions. In order to get higher deformation values an annealed condition is proposed to form the material. The effect of T6 heat treatment and O annealing treatment in the uniaxial warm formability is discussed and a microstructural analysis is also presented in order to understand the differences on the alloy behaviour.

Abstract: Semisolid forging process requires special movement of the ram, until now only achievable with hydraulic presses. The upper die, placed on the press ram, must move fast during forming of the component in order to reduce segregation phenomena, and, once the part is shaped, the die must squeeze the material so that the contraction of the material is overcome and no shrinkage defects are formed. Traditional mechanical presses are not able to reproduce this kind of cycles, only possible with hydraulic presses. The introduction of servo motors in mechanical presses makes possible the achievement of those requirements, and, therefore, the use of these presses for the semisolid forging processes. The main characteristic of this type of machines is the elimination of the flywheel and the clutch; in the solution proposed by the press builder Fagor, the AC servo motor drives the ram of the press by using a transmission based on gears and a crank. This paper presents some of the results achieved during the semisolid forging of A356 aluminium alloy using a 400 tons Fagor servo motor driven mechanical press installed at the University of Mondragon.

Abstract: Extrusion is a well established technology for the production of complex sections of aluminium alloys. Thixo-extrusion in comparison to traditional hot-extrusion offers several advantages such as lower extrusion and friction forces, higher material fluidity, longer tool life etc. Aluminium alloy 5182 is an important commercial alloy characterized by high strength and ductility, high corrosion resistance and good formability; it is commonly used for the production of wrought automotive components and it is also suitable for semi-solid applications thanks to its wide solidification range. The aim of this paper is to attempt the shaping of 5182 Al-Mg alloy through the thixo-extrusion process using a ceramic tool and evaluating the effect of different routes of making the feedstock on the semisolid microstructure. Particularly, two different methods were investigated: Near-solidus casting and Roll-casting using a cooling slope. All the samples produced were characterized by metallographic analysis in order to measure globule size and shape factor, as the main criteria used for assessing thixo-formability.

Abstract: The achievement of lighter automotive components is an important driving force in the development and optimization of casting techniques. In this sense, semisolid forming is an emerging technology that has allowed the production of security components using aluminum alloys. The foundry alloys A356 and A357 remain, up to the present, the most used alloys for the semisolid processing of components. Nevertheless, several authors have pointed out the gain in properties that other alloy families could provide. In the present work, thixoformability of 7000 series aluminum alloys is studied. Thermodynamic calculations (CALPHAD method) and calorimetric experiments have been performed to determine the composition of alloys with an optimum process window. A modification of the 7075 alloy is proposed in order to improve its thixoformability parameters and optimize the process control. A simple component has been produced by semisolid forging and mechanical properties have been measured from tensile samples.