Laser-induced softening analysis of a hardened aluminum alloy by physical simulation

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.

Study of Tailored Hot Stamping Process on Advanced High-Strength Steels

“…Preliminary tests have shown that a cooling rate of 25 K/s is enough to characterize the material in austenitic field even at the lowest temperature and strain rate investigated. The respect of this cooling rate without the use of forced air has been obtained performing the specimen design with a FE model developed in COMSOL Multiphysics [12].…”

Physical Simulation of Laser Surface Treatment to Study Softening Effect on Age-Hardened Aluminium Alloys

“…Since these are rapid thermal cycles, to satisfy the cooling rate during Gleeble tests, a tapered specimen was adopted. The geometry of specimens was defined thanks to optimization of the length and width of the shaped area studied in the previous work [12]. Physical simulation tests were carried out on the tapered specimens that were subjected to the subsequent micro-hardness test, and on notched specimens that were subjected, instead, to the subsequent tensile test.…”

“…The results acquired from the thermocouples were used to estimate the peak temperature profile thanks to a thermo-electric, 3D, transient, finite-element model developed in COMSOL Multiphysics [12]. The FE model couples the thermal and electrical fields.…”

“…In fact, as previously highlighted, the maximum softening conditions were not reached in the central area. To highlight the specimen region of the maximum softening, a procedure that estimates the material micro-hardness value as a function of the peak temperature reached in the physical simulation test was implemented in the thermoelectric FE model [12]; in this procedure, the micro-hardness value was calculated using the polynomials reported in Table 5.…”

“…Figure 25 shows the results obtained with the FE model for the T510V5 thermal cycle, using the interpolation polynomial estimated in the T4 state. The temperature and microhardness profiles highlighted in Figure 25a show that the specimen area that reaches the To highlight the specimen region of the maximum softening, a procedure that estimates the material micro-hardness value as a function of the peak temperature reached in the physical simulation test was implemented in the thermoelectric FE model [12]; in this procedure, the micro-hardness value was calculated using the polynomials reported in Table 5.…”