Issue 35

A. Kowalski et alii, Frattura ed Integrità Strutturale, 35 (2015) 449-455; DOI: 10.3221/IGF-ESIS.35.51 455 C ONCLUSIONS he performed investigations concerning the fatigue of the AlZn6Mg0.8Zr alloy 7003 series and the analysis of the results of the mechanical properties, as well as metallographic observations allow to draw the fallowing conclusions: 1. The fatigue strength of the tested samples of aluminium of the kind 7003 subjected to low-temperature thermomechanical treatment changes linearly within the range of low-cyclic loads from the value of stresses σ a amounting to about 190 MPa to about 160 MPa, corresponding to the number of cycles of oscillating bending N f from about 6·10 4 to about 2·10 6 . 2. The applied variant of thermomechanical treatment affects positively the refinement of the grains in the solution-α of the investigated alloy and increases the amount and dispersion of precipitations of intermetallic phases, mainly of the Mg 2 Si or Al 2 Mg type. 3. The fractures of the tested samples are after fatigue tests in the range of low-cyclic temporary fatigue strength principally transcrystalline quasi-cleavage with the cleavage planes without any traces of plastic deformation and zones of intercrystalline cracking. 4. In the zone of high-cycling fatigue and permanent fatigue strength the fractures of the tested samples indicate a distinct share of plastic deformation on the surface of the jogs affecting potentially the stochastic planes of cleavage. 5. The microfractography of fatigue fractures of the analyzed samples indicate probably an interlocking mechanism of cracking of the Al-Zn-Mg alloy. REFERENCES [1] Oczoś, K.E., Kawalec, A., Formation light metals, Publ. PWN, Warsaw (2012), in Polish. [2] Bernstein, M.L., Thermomechanical treatment of metals and its alloys, T. 1. Publ. Metallurgy Moscow, (1968), in Russian. [3] Jurczak, W., Safety Exploitation of Aluminum Technical Constructions in the Aspect of Seawater Environment Influence, Polish Journal of Environmental Studies, 14(I) (2005) 180-185. [4] Jurczak, W., The effect of heat treatment on the structure and corrosion resistance of Al-Zn-Mg alloys, Polish Maritime Research, 4(58) (2008) 66-71. [5] PN-EN 573-3, Aluminium and its alloys. Part 3 (2014). [6] Kurek, A., Niesłony, A., Fatigue Life Tests of Explosively Cladded Steel-Titanium Bimetal, Materials Science Forum, 726 (2012) 106-109. [7] Starke, E.A., Staley, J.T., Application of Modern Aluminium Alloys to Aircraft, Prog. Aerosp. Sci., 32 (1996) 131-172. T