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Abstract

The continuous needs of improve performances in the automotive sector in terms of dynamic behaviour, fuel consumption and safety of passengers, have raised the interest for lightweight alloys as well as for the optimization of the design of the structural components of the car chassis. With this twofold aim, many researches are focused in the evaluation of new car designs, materials, and processes to manufacture even more complex components with increased stiffness-to-weight ratio. From that standpoint, the use of shaped hollow parts in the car body in white appears one of the most promising solutions, due to the elevated stiffness of tubular structures and the reduced weight. However, hydroforming processes that have been traditionally used to shape such components have shown several limitations with lightweight alloys, suffering their reduced formability, the temperature limitations of the forming liquids as well as long process time and complex machines. In this paper the recently introduced technology of Hot Metal Gas Forming (HMGF) has been considered, in order to investigate the influence of the process parameters on the formability of AA6060 tubes. The semi-finished tubes were produced through direct hot extrusion, with different temperatures and feed rates process, and tested by HMGF at elevated temperatures. The properties of the final products are investigated through analyses of the microstructure, micro hardness and thickness measurements.
Formability of AA6060 tubes in hot metal gas forming at high
temperatures
Francesco Michieletto1,a, Andrea Ghiotti1,b and Stefania Bruschi1,c
1Department of Industrial Engineering, University of Padua, Via Venezia 1, 35131, Padua, Italy
afrancesco.michieletto@dii.unipd.it, bandrea.ghiotti@unipd.it, cstefania.bruschi@unipd.it
Keywords: hot deformation, metal forming, hot metal gas forming.
Abstract. The continuous needs of improve performances in the automotive sector in terms of
dynamic behaviour, fuel consumption and safety of passengers, have raised the interest for
lightweight alloys as well as for the optimization of the design of the structural components of the
car chassis. With this twofold aim, many researches are focused in the evaluation of new car
designs, materials, and processes to manufacture even more complex components with increased
stiffness-to-weight ratio. From that standpoint, the use of shaped hollow parts in the car body in
white appears one of the most promising solutions, due to the elevated stiffness of tubular structures
and the reduced weight. However, hydroforming processes that have been traditionally used to
shape such components have shown several limitations with lightweight alloys, suffering their
reduced formability, the temperature limitations of the forming liquids as well as long process time
and complex machines. In this paper the recently introduced technology of Hot Metal Gas Forming
(HMGF) has been considered, in order to investigate the influence of the process parameters on the
formability of AA6060 tubes. The semi-finished tubes were produced through direct hot extrusion,
with different temperatures and feed rates process, and tested by HMGF at elevated temperatures.
The properties of the final products are investigated through analyses of the microstructure, micro
hardness and thickness measurements.
Introduction
The last decade has seen a continuous demand of increased structural performances in
automotive, to improve the dynamics behaviour of cars, the chassis stiffness-to-weight ratio, the
passengers safety as well as to reduce the fuel consumption and, consequently, the emission of
pollutions to contrast the effects on the global environment. Such trends have been strengthened by
new regulations established by EU and US commissions after the Kyoto protocol entered into force
in 2005, with challenging targets in term of control of fuel emissions to be reached within the 2020s
[1]. With such goals, automotive industries are continuously working on innovations of both the
engines and the structural parts of the car-body-in-white: the former towards the integration of more
efficient and electricity-driven technologies, the latter characterized by the optimization of materials
and structures, even through the introduction of new concepts and designs.
One of the most recent trends is represented by the use of light alloy complex shaped hollow
parts in the manufacturing of the car chassis, which allows a significant increase of the stiffness
compared to sheet metal components together with the reduction of the total car weight. The
AA6xxx series have proved to be among the best candidates to replace steels due to their low
weight, good strength, corrosion resistance, weldability and paintability [2]. In traditional process
chains to form hollow components, metal tubes are obtained by direct or indirect hot extrusion, and
then hydro formed at room temperature to take advantage of the increase of formability allowed by
the hydrostatic pressure [3]. In addition increasing the temperature during the hydroforming process
is possible to increase the material formability, especially for the lightweight materials like
aluminium alloys [4], and decrease the pressure of the liquid used to shape the component.
Moreover, through an optical measure system is also possible to find the best hydroforming
condition of the initial material, in terms of temperature and pressure [5], to evaluate the tube
Key Engineering Materials Submitted: 2014-10-14
ISSN: 1662-9795, Vol. 639, pp 49-56 Revised: 2014-12-17
doi:10.4028/www.scientific.net/KEM.639.49 Accepted: 2015-01-14
© 2015 Trans Tech Publications Ltd, Switzerland Online: 2015-03-20
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