Conception of tooling adapted to thixoforging of high solid fraction hot-crack-sensitive aluminium alloys

Thixoforging is a type of semi-solid metal processing at high solid fraction (0.7<φs<1), which involves the processing of alloys in the semi-solid state.Tooling has to be adapted to this particular process to benefit shear thinning and thixotropic behaviour of such semi-solid material.Tooling parameters, such as the forming speed and tool temperature, have to be accurately controlled because of their influence on thermal exchanges between material flow and tool.These thermal exchanges influence the high-cracking tendency and the rheology of the semi-solid material during forming, which affects parts properties and therefore their quality.Extrusion tests show how thermal exchanges influence quality of thixoforged parts made of 7075 aluminium alloys at high solid fraction by modifying process parameters like forming speed, tool temperature and tool thermal protector.Thus an optimum in terms of thermal exchanges has to be found between surface quality and mechanical properties of the part.A direct application is the evaluation of surface quality of thixoforged thin wall parts made of 7075 aluminium alloy.

Stability of steel thixoforming process

To improve the industrialization of the process,the study of a thixoforming line stability was proposed.The thixoforming line is fully automated to optimize the repeatability of the experiments.Parameters of the heating cycle,the slug temperature,the tool temperature and the forming speed were studied.For each of them,a range of the expected variations in a steady-state process as well as the effects of these variations on the process itself(forming load and parts quality) were given.These variations are shown to be acceptable.Three different tools were used in the experiments.Some mathematical simulations were realized on the finite elements code Forge2008with a semi-solid constitutive law.The capacity of the model to represent the process stability was discussed.The simulation results are in agreement with the experiment results.

Characterization of thixoforming process of 100Cr6 steel

The main goal of this work is to analyze the semi-industrial process of steel thixoforming.The process was carried out using industrial equipment.This equipment consists of a heating device,industrial robots and a hydraulic press.The globular microstructure ensuring thixotropic properties was obtained using the SIMA method.It is one of the simplest and cheapest methods which could be easy applied in the case of steel alloys.In this work,the hot forged rods,commercially produced from 100Cr6 steel,were used.The first part of the work concerned the determination of the proper temperature range,for thixoforming of 100Cr6 steel.Next,some heating tests were carried out in order to obtain as uniform temperature distribution as possible.Heating process was executed using inductive heating.Microstructure analysis of heated samples reveals globular particles surrounded by liquid phase.At last,the thixoforming process was carried out using closed-die forming technique.Completely filled die cavity and good microstructure of the part show that applied process parameters were properly selected.

X38CrMoV5 hot-work tool steel as tool material for thixoforging of steel:Numerical and experimental evaluation

Although thixoforming of low melting point alloys as aluminum or magnesium is now an industrial reality,thixoforming of high melting point alloys as steel is still at the research level.High working temperature,die wearing and production rate are problems that must be solved and are under investigation.The aim of this work is to evaluate the thermal and mechanical loadings applied to the tools during the steel thixoforging process in order to determine whether classical hot-work tool steel can be an appropriate tool material.This evaluation has been realized thanks to experimental trials and to simulations on the finite elements code Forge2008.The effect of the loadings on the tool's failure modes are highlighted and compared with the ones observed in classical hot forging.Beyond this,the failure modes of hot-work tool steel,the X38CrMoV5 or H11,were presented.

Thixoextrusion of A357 aluminium alloy

The aim of this work is to attempt the application of A357 Al-Si-Mg cast alloy in the thixoextrusion process,evaluating the different forming parameters effect.Thixoextrusion offers several advantages compared with traditional hot-extrusion such as lower pressure,minor friction forces,higher material fluidity and longer tool life.This type of semi-solid process requires high solid fraction(0.7<fs<1) materials because of its low solidification rate.Aluminium alloy A357 is a commercial cast alloy characterized by high strength,ductility and corrosion resistance.It is commonly used for cast production of automotive components and it is also suitable for semi-solid process,due to its wide range of solidification.A357 aluminium alloy was used as a feedstock for thixoextrusion in order to investigate thixoformability at high solid fraction.A357 alloy with high solid fraction(>0.85) is less sensitive to temperature drops and allows more stable material flow at higher speeds.To know the forming parameters that improve the mechanical properties of thixoextruded parts,some extrusion tests were carried out.The results were used as the main criteria for assessing the thixoforming viability of the A357 alloy.