Einfluß der Porosität auf das Schwingfestigkeitsverhalten von Aluminium-Gußwerkstoffen

In this work the age hardened alloys G-AlSi 7 Mg 0.6 wa, G-AlCu 4 Ti wa as well as the untreated G-AlSi 11 MgSr, G-AlSi 11 Mg and G-AlSi 11 Sr had been investigated. The results indicate that in spite of the great differences in tensile strengths depending on whether age-hardened or not, the endurance limits are found to be in quite the same range. The age-hardened alloys can be recommended not only for use in the region of the endurance limit, but also because of the steep course of the S-N-curves for finite fatigue life and variable amplitude applications. The not age-hardened alloys should be applicated in the region of endurance limit only because the shallow course of their S-N-curves. The cyclic material behaviour of all investigated alloys had been determined as hardening when the yield stress is exceeded repeatedly. The influence of degree of porosity on fatigue strength could be verified: If the degree of porosity due to ASTM E 155 is increased from 0 to 8, the fatigue strengt h is decreased by about 17 % concerning all regarded alloys in the unnotched state. In the notched state the reduction of fatigue strength was determined as 7 % for the age-hardened alloys but as 20 % for the not age-hardened alloys. The latter is due to the lower yield strength values of these materials. An influence of the thickness of the solidified cross section could not be determined. With regard to the resemblance of the depicted results of both age-hardened alloys, the alloys G-AlCu 4 Ti wa, which has been proved to be technically problematic in casting, can be replaced by the alloy G-AlSi 7 Mg 0.6 wa.