Issue 35

A. Kowalski et alii, Frattura ed Integrità Strutturale, 35 (2015) 449-455; DOI: 10.3221/IGF-ESIS.35.51 449 Focussed on Crack Paths Fatigue cracking of aluminium alloy AlZn6Mg0.8Zr subjected to thermomechanical treatment A. Kowalski, W. Ozgowicz Silesian University of Technology, Poland aleksander.kowalski@polsl.pl M. Kurek, A. Kurek, T. Łagoda Opole University of Technology, Poland a.kurek@po.opole.pl A BSTRACT . The paper presents the results of experimental test of the fatigue of aluminium alloy type AlZn6Mg0,8Zr exposed to various low temperature thermomechanical treatment. Basquin’s characteristics of fatigue have been determined in mechanical test on smooth specimens at a simple state of loading in conditions of alternating bending. The tests were carried out on a fatigue test stand constructed by the authors – MZGS 100. The development of fatigue cracking has been described based on metallographic and fractographic investigations of the fractured samples making use of a scanning electron microscope (SEM). The results of qualitative microfractography of the tested samples in the low-cycle temporal range of fatigue strength revealed fractures of the transcrystalline quasi-cleavage type. It has also been found that local effects of intercrystalline brittle cracking of this type do occur. K EYWORDS . Aluminium alloy; Fatigue tests; Thermomechanical treatment; Fatigue cracking; SEM. I NTRODUCTION luminium alloys as well as their technology constitute an important position in the design and construction of light but highly resistant structures in many branches of industry, both civilian industry and that producing military equipment. A reduction of the mass of vehicles and the consumption of fuel, a higher carrying capacity, less expensive and safest structures, and also ecological aspects are actually the fundamental criteria in the choice of adequate material, not only in the automotive and aircraft industry, but also in ship-building and the production of machines structures of transport. This requires a constant development in the technology and improvement of the properties of aluminium alloys, resulting in a higher effectiveness in various applications. Thanks to their high relative strength (R m / ρ ) and resistance to impacts, their inurement to brittleness, non-magnetic (paramagnetic material) and good resistance to corrosion in a marine environment, these alloys are applied, among others, in the shipbuilding, particularly of a fast non-displacing vessels, such as landing crafts, rocket cutters, submarines, hydrofoil boats and other vessels carrying considerable dynamic and fatiguing loads, as well as touristic and sport units. An essential problem of the technology of aluminium alloys is not only the formation of their mechanical properties, but also their formation by means of casting, plastic deformation, freeform fabrication or machining [1]. One of the effective A