I. Hurtado

Experimental and Numerical Study of Electromagnetic Forming of AZ31B Magnesium Alloy Sheet

Wrought magnesium alloys are interesting materials for automotive and aeronautical industries due to their low density in comparison to steel and aluminium alloys, making them ideal candidates when designing a lower weight vehicle. However, due to their hexagonal close-packed (hcp) crystal structure, magnesium alloys exhibit low formability at room temperature. For that reason, in this study a high velocity forming process, electromagnetic forming (EMF), was used to study the formability of AZ31B magnesium alloy sheet at high strain rates. n n n nIn the first stage of this work, specimens of AZ31B magnesium alloy sheet have been characterised by uniaxial tensile tests at quasi-static and dynamic strain rates at room temperature. The influence of the strain rate is outlined and the parameters of Johnson-Cook constitutive material model were fit to experimental results. In the second stage, sheets of AZ31B magnesium alloy have been biaxially deformed by electromagnetic forming process using different coil and die configurations. Deformation values measured from electromagnetically formed parts are compared to the ones achieved by conventional forming technologies. Finally, numerical study using an alternative method for computing the electromagnetic fields in the EMF process simulation, a combination of Finite Element Method (FEM) for conductor parts and Boundary Element Method (BEM) for insulators, is shown.

Thixo-Extrusion of 5182 Aluminium Alloy

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.

Rheological characterization of A201 aluminum alloy

The thermodynamic characterization as well as the rheological characterization of the A201 alloy were conducted. Thermodynamic simulations (CALPHAD method) and calorimetric experiments were performed to determine the solidus and liquidus temperatures, the melting range and the sensitivity of the solid fraction at the thixoforming temperatures. The rheology of aluminium alloy A201 was examined using a high temperature Searle rheometer. The flow behaviour was analyzed with concentric cylinders of graphite to avoid chemical interactions with the liquid or semi-solid aluminium. The rotational body was grooved to prevent a phenomenon called wall slippage. Continuous cooling experiment was used to observe the shear rate effects on the flow behaviour. It can be seen that the viscosity level decreases at higher shear rates. Shear rate jump experiment was carried out to evaluate the steady state flow curve within the analyzed shear rate range from 60 s −1 to 260 s −1 . It is found that the power law indexes are −1.35 and −1.49 for 35% and 45% solid fraction, respectively. Finally, some mechanical property data of as-cast and as-thixoformed A201 alloy are included indicating the potential for high strength applications.

Effectivity of fluoride treatment on hydrogen and corrosion product generation in temporal implants for different magnesium alloys.

The increasing interest on magnesium alloys relies on their biocompatibility, bioabsorbility and especially on their mechanical properties. Due to these characteristics, magnesium alloys are becoming a promising solution to be used, as temporary implants. However, magnesium alloys must overcome their poor corrosion resistance. This article analyses the corrosion behaviour in phosphate-buffered saline solution of three commercial magnesium alloys (AZ31B, WE43 and ZM21) as well as the influence of fluoride treatment on their corrosion behaviour. It is shown that the corrosion rate of all the alloys is decreased by fluoride treatment. However, fluoride treatment affects each alloy differently.

Thixo Lateral Forging of a Commercial Automotive Spindle from LTT45 Steel Grade

The present paper is focused on the thixo lateral forging of a nearly 3 Kg commercial automotive spindle. A thixoforming cell has been implemented in the forming lab consisting on an induction unit, six-axes industrial robot for the handling tasks and a servo-mechanical forming press. A special tool has also been designed in order to use all the press capacity during the forming stage. First trials have been made using LTT45 steel. The usual material for this spindle fabrication is a CrMo alloyed steel (W-Nr 1.7225) employed in automotive components with high requirements on toughness. The selected thixoforming steel has been modified to have a wider solidification range and lower solidus temperature.

Servomechanical Press: A New Press Concept for Semisolid Forging

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.

New Forming Limits For Light Alloys By Means Of Electromagnetic Forming And Numerical Simulation Of The Process

It is well known that one of the main advantages of the high speed forming (HSF) processes is the improvement in the forming limits of the used materials.Using the Electromagnetic Forming (EMF) technology two materials have been tested with different mechanical and physical properties: the AA5754 aluminium and the AZ31B magnesium alloys.The EMF process principle can be described as follows: A significant amount of electrical energy is stored in a bank of capacitors which are suddenly discharged releasing all the stored energy. This electric discharge runs through a coil which generates an intense transient magnetic field. At the same time transient Eddy currents are induced in the electrically conductive part placed some millimetres far from the coil. Another intense magnetic field is generated due to those Eddy currents but on the opposite direction as the one generated by the coil. A big magnetic repulsion force is created between the part and the coil. This magnetic repulsion between both fields is use...

Analysis of a Thixo-Lateral Forged Spindle from LTT C45, LTT C38 and LTT 100Cr6 Steel Grades

Due to the current trend in prices of raw material and their sources, near net shaping of mechanical components will become a key factor for the companies to get the desired competitiveness. Semisolid metal (SSM) forming is one of those near net shape forming techniques revealing a high potential to reduce material as well as energy consumption compared to conventional process technologies. Thus, the aim of this research work is to demonstrate the above by manufacturing a steel commercial automotive spindle by thixo-lateral forming from three different steel grades. The starting material, the microstructure and mechanical properties are analysed along the article. Material savings of 20% have been reported together with a substantial decrease of the forming forces. In addition, great mechanical properties have been achieved which brings the process closer to the desired final industrial application.

Texture Evolution of AZ31 Magnesium Alloy Sheet at High Strain Rates

In the current contribution the mechanical behaviour at high strain rates of AZ31 magnesium alloy sheet is studied. Uniaxial deformation properties were studied by means of tensile split Hopkinson pressure bar (SHPB) at different temperatures. The influence of the strain rate and temperature on the deformation mechanisms was investigated by means of electron backscatter diffraction (EBSD) and neutron diffraction. It is shown that twinning plays an important role on high strain rate deformation of this alloy, even at elevated temperatures. Significant evidence of prismatic slip as a deformation mechanism is observed, also at warm temperatures, leading to the alignment of directions with the tensile axis and to a spread of the intensities of the basal pole figure towards the in-plane direction perpendicular to the tensile axis. The rate of decrease of the CRSS of non-basal systems is observed to be slower than at quasi-static rates. Secondary twinning and pyramidal slip were also outlined for some conditions. At warm temperatures, in contrast to quasi-static range, a generalized dynamic recrystallization is not observed. Moreover, the activation of rotational recrystallization mechanisms is reported

Semisolid Forging of 7000 Series Aluminum Alloys

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.