Effects of charge composition on microstructure, mechanical and fatigue properties of nodular cast irons have been studied. For experiments, five melts of nodular cast iron were used – three types of unalloyed nodular cast irons (with different ratio of steel and pig iron in a charge and different additives for regulation of the chemical composition) and two types of alloyed nodular cast irons (SiMo- and SiCu- nodular cast iron). The microstructure of the specimens was evaluated according to a norm and by automatic image analysis. The mechanical properties were investigated by the tensile test, impact bending test and Brinell hardness test. The fatigue tests were carried out at sinusoidal cyclic push-pull loading at ambient temperature. The best mechanical properties were reached in the nodular cast iron alloyed by Si and Cu, what is related to its microstructure.
This article deals with the fatigue properties of newly used AlZn10Si8Mg aluminium alloy where the main aim was to determine the
fatigue strength and compare it with the fatigue strength of AlSi7Mg0.3 secondary aluminium alloys which is used in the automotive
industry for cyclically loaded components. AlZn10Si8Mg aluminium alloy, also called UNIFONT 90, is self-hardening (without heat
treatments), which contributes to economic efficiency. This is one of the main reasons why is compared, and may be an alternative
replacement for AlSi7Mg0.3 alloy which is heat treated to achieve required mechanical properties. The experiment results show that the
fatigue properties of AlZn10Si8Mg alloy are comparable, if not better, than AlSi7Mg0.3 alloy. Fatigue properties of AlZn10Si8Mg alloy
are achieved after seven days of natural ageing, immediately after casting and achieving value of fatigue strength is caused by structural
components formed during solidification of the melt.
The effect of combination grain refinement with AlTi5B1 master (55 ppm) and Sr-modification with AlSr5 master (20, 30, 40, 50 and 60 ppm) on the microstructure, tensile and hardness properties of AlSi7MgTi cast alloy were systematically investigated. Eutectic silicon was studied by optical and scanning electron microscopy after standard (0.5% HF) and deep etching (HCl). Morphology of eutectic Si changes from compact plate-like (as-cast state) to fibbers (after modification). Si-fibbers in samples with 50 and 60 ppm Sr coarsen probably as a result of over-modification. The optimum mechanical properties has the experimental material which was grain refined and modified with 40 ppm of Sr (UTS = 220.6 MPa; ductility = 6.1%, and 82.3 HBW 5/250/15).
The secondary aluminium alloys are very important material in actual industry from economic and ecological point of view. The secondary aluminium used for production of casts, however, contains some elements, i.e. iron, – affecting physical, chemical and mechanical behaviour. The subject of our investigation has been corrosion behaviour in natural atmosphere of the hypoeutectic AlSi7Mg0.3 cast alloys with various content of iron, because the Fe content affects not only mechanical properties but corrosion resistance, as well. Three types of the AlSi7Mg0.3 cast alloys were exposed for 9 months in natural atmosphere and the measure of their degradation by corrosion was found by determination of the weight loss and the light microscopy. In addition, a scanning electron microscopy (SEM) analyses and evaluation of surface changes were used. The corrosion behaviour in natural atmosphere was compared to results of the carried out electrochemical and exposure laboratory experiments in chloride solutions.