No abstract

No abstract

The effect of microstructure on the work-hardening and ductile fracture of aluminium alloys was studied using an experimental-numerical approach. Four aluminium alloys with different strength and particle content were tested in uniaxial tension after the following subsequent processing steps: 1) casting and homogenization, 2) extrusion, and 3) cold rolling followed by heat treatment. The latter processing step was carried out to obtain a recrystallized grain structure with random crystallographic texture. The alloys were two AlFe alloys with different Fe content, one AlMn alloy and one AlMgSi alloy. The grain structure, particle distribution and crystallographic texture were determined for all combinations of alloy and processing route using optical and scanning electron microscopy. Tensile tests were carried out on axisymmetric samples to obtain the true stressstrain curves to failure and the true failure strain of the materials, using a laser-based measuring system. Based on numerical simulations of the tensile tests, the equivalent stress-strain curves were determined to failure, assuming J 2 flow theory. The results showed that the microstructure had a marked effect on both work-hardening and ductility, while the ductile fracture mechanism remained unchanged. The plastic anisotropy, induced by the extrusion process and not entirely removed by the cold rolling and heat treatment, led to a wide range of fracture modes of the axisymmetric samples. The failure strain was markedly lower for the cast and homogenized material than for the extruded and the cold rolled and recrystallized materials of the same alloy. The failure strain was further found to decrease linearly with the yield stress for similar microstructure.

No abstract

No abstract

Experiments were conducted to attempt to understand the effect of different alloying elements on the ductility of Al-Mg-Si alloys. Four alloys with different concentrations of Si, Mg, Fe, Mn and Cu were selected for examination. The strength-ductility relationship was evaluated by tensile tests, and microscopic analysis in light optical microscope, SEM and TEM was conducted to investigate grain-, constituent-, precipitatation-and fracture characteristics.Excess-Si (Mg/Si>1.73) was found to have a detrimental effect on the ductility of Al-Mg-Si alloys, without the presence of additional alloying elements. This alloy had an elongation to fracture of 23.1%, where failure occurred partly intergranularly, and was seemingly due to poor grain boundary characteristics. Adding Fe and Cu improved the ductility (and strength) to 42.9% elongation, and the change was related to the formation of secondary-phase particles, resulting in less free Si for embrittlement of grain boundaries. The best ductility, 79.2% elongation, was found by introducing Mn, which in addition to the above-mentioned changed the recrystallization behavior.The most desirable combination of tensile strength (456 MPa) and ductility (64.6%) was found in a balanced alloy (Mg/Si~1.73) with an addition of both Mn and Cu. Primarily, Cu was associated with an increase in strength, by changing the precipitation behavior and precipitate characteristics. Mn contributed to both an increase in strength and ductility, by formingThe Influence of Alloying Elements on the Ductility of Al-Mg-Si Alloys Remøe, M. S.

Previous investigations of the penetration and perforation of high-strength steel plates struck by hardened steel projectiles have shown that under certain test conditions the projectile may fracture or even fragment upon impact. Simulations without an accurate failure description for the projectile material will then predict perforation of the target instead of fragmentation of the projectile, and thus underestimate the ballistic limit velocity of the target plate. This paper presents an experimental investigation of the various deformation and fracture modes that may occur in steel projectiles during impact. This is studied by conducting Taylor bar impact tests using 20 mm diameter, 80 mm long, tool steel projectiles with three different hardness values (HRC 19, 40 and 52). A gas gun was used to fire the projectiles into a rigid wall at impact velocities ranging from 100 -350 m/s, and the deformation and fracture processes were captured by a high-speed video camera. From the tests, several different deformation and fracture modes were registered for each hardness value. To investigate the influence of material on the deformation and fracture modes, several series of tensile tests on smooth axisymmetric specimens were carried out to characterise the mechanical properties of the three materials. To gain a deeper understanding of the various processes causing fracture and fragmentation during impact, a metallurgical investigation was conducted.The fracture surfaces of the failed projectiles of different hardness were investigated, and the microstructure was studied for each hardness value.

The work-hardening and ductility of an artificially aged AA6060 aluminium alloy were studied based on tensile tests of smooth and notched cylindrical samples. The alloy was tested after three processing steps, each followed by artificial aging. These processing steps were casting and homogenization, extrusion, and cold rolling and heat treatment to obtain a recrystallized grain structure. Subsequent to each of these processing steps, the material was tested after artificial aging to underaged, peak aged and overaged conditions. The true stress-strain curve to failure was determined by use of a laser-based measurement system. The Bridgman correction was applied to estimate the equivalent stress-strain curves, and the work-hardening behaviour was analysed using an extended Voce approach. Fractography was applied to study the failure mechanisms for material exposed to the different processing steps and temper treatments. To evaluate the use of the Bridgman correction and to study the notch strengthening effect observed experimentally, finite element simulations were performed using the Gurson model. By comparing the three processing steps, the effects of the texture on the strength and work-hardening were obtained experimentally for the three tempers. The effect of particle size, shape and distribution on the failure strain was observed.