Abstract
The study focuses on the analysis of the softening effects of the work-hardened aluminum alloy sheets EN AW 5754 H32 1.5 mm thick, through the physical simulation of thermal cycles induced in the material by laser heat treatments (LHTs). A numerical-experimental approach was implemented to define the laser thermal cycles and to subsequently reproduce them on the GleebleTM 3180 physical simulator. The obtained softening was measured by microhardness and metallographic analysis tests. For the definition of laser thermal cycles, preliminary tests with a 2.5 kW CO2 laser source have been realized, and a three-dimensional transient finite element thermal models were developed and calibrated with the experimental results. The investigated laser heat treatment parameters explored thermal cycles with different shape, interaction time, and peak temperature. Physical simulation tests were performed using laser thermal cycles that showed the maximum softening of the aluminum alloy. A three-dimensional transient finite element thermoelectric model was developed to design the shape of the Gleeble specimens, which satisfy the heating and cooling rate required by laser thermal cycles. Results obtained show that it is possible to physically simulate the investigated laser thermal cycles, reducing the cross section of the shaped part of the specimen. Softening effects depend on the thermal cycle shape. Greater softening is observed by increasing the interaction time and the peak temperature, but beyond a peak temperature threshold value, negligible effects are detected.
Highlights
Interest in the local softening using laser heat treatment process is growing in recent period because it offers the possibility to process metal alloy sheets locally, creating areas with defined mechanical properties
The physical simulation tests were carried out with the Gleeble 3180 system for some of the thermal cycles acquired with laser thermal treatments. (iii) The metallographic analysis was performed with microhardness tests on laser and Gleeble specimens to evaluate the softening effects induced by thermal cycles; electrochemical etching tests were performed to analyze the effect of heat treatments on the grain size
The methodology has been applied for the local softening of the EN AW 5754 H32 work-hardened aluminum alloy sheet of 1.5 mm thickness; softening was evaluated by microhardness tests
Summary
Interest in the local softening using laser heat treatment process is growing in recent period because it offers the possibility to process metal alloy sheets locally, creating areas with defined mechanical properties. In this latter process, known as Tailored Heat Treated Blank (THTB), the laser heat treatment enables the local tailoring of the material properties [4]. It is necessary to evaluate the influence of laser thermal cycles on the material properties, making careful assessments of the process parameters before starting a process on an industrial scale. For this purpose, physical simulators such as Gleeble systems allow to reproduce thermomechanical cycles typical of manufacturing processes, in the severe condition realized by laser heat treatments (thermal cycles with higher heating and cooling rate). Laser heat treatments can lead to distortion phenomena that can be avoided by using Gleeble system, obtaining more correct evaluations
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