Dynamic failure mechanism of copper foil in laser dynamic flexible forming

Abstract

Laser dynamic flexible forming (LDFF) is a novel high velocity forming (HVF) technology, in which the foil metal is loaded by laser shock wave. Strain localization is readily to occur around the bulge edge, which will result in the ultimate dynamic failure. In this work, the microstructures before and after dynamic fracture are characterized by transmission electron microscopy (TEM) to investigate the dynamic failure mechanism. The plastic deformation regions of copper foil are composed of shock compression, strain localization and bulge. Microstructure refinement was observed in three different plastic deformation regions, particularly, dynamic recrystallization (DRX) occurs in the strain localization and bulge regions. In bulge region, extremely thin secondary twins in the twin/matrix (T/M) lamellae are formed. The microstructure features in the strain localization region show that superplastic flow of material exists until fracture, which may be due to DRX and subsequent grain boundary sliding (GBS) of the recrystallized grains. The grain coarsening in strain localization region may degrade the material flowing ability which results in the dynamic fracture.

Warm sheet metal forming of energy-absorbing elements made 7075 aluminum alloy in the hardened state T6

“…Heating the material to temperatures above 260 °C causes permanent microstructural changes, reducing the final product's mechanical properties. It should also be noted that the elevated temperature increases the material's strain rate sensitivity and the friction coefficient between the sheet and the tools [14]. The study on the 7000 series alloys carried out by Kumar et al shows that the most favorable forming temperature is 250 °C as it dissolves the metastable precipitations, which are responsible for high strength and low formability [15].…”