MECHANIK NR 11/2017  Fatigue resistance of AlSi11 alloy plastically wedged of chips Odporność zmęczeniowa stopu AlSi11 konsolidowanego plastycznie z wiórów ŁUKASZ WZOREK MATEUSZ WĘDRYCHOWICZ TOMASZ SKRZEKUT PIOTR NOGA MARCEL WIEWIÓRA MATEUSZ PACEK * DOI: https://doi.org/10.17814/mechanik.2017.11.181 Two extrudates made of AlSi11 alloy have been produced in the co-extrusion process: solid billet and machining chips from the rolling process. The microstructure was observed, mechanical properties were determined on the basis of the 1- axial stretch test, and the fatigue tests were performed to determine the fatigue resistance of the AlSi11 alloy. KEYWORDS: AlSi11, plastic consolidation, fatigue test In Al-Si alloys, such as additives Fe, Mn and Sr have a strong influence on the fatigue properties of these materials [1]. For example, the addition of iron significantly reduces fatigue resistance, because it creates β-15FeSi intermetallic compound. In addition, manganese improves fatigue strength, while strontium improves both impact strength and fatigue resistance [1]. High temperatures adversely affect the fatigue strength of metals and their alloys. In case of AlSi12CuNiMg alloy, a marked decrease in resistance is visible after annealing at temperatures above 200°C. This is due to the disappearance of the consolidation due to premature aging and the coalescence of the Guinier- Preston (GP) zones during heating [2]. Similarly, Nicoletto et al. [3] investigated the effect of temperature on the fatigue resistance of eutectic Al-Si alloys. Test specimens cut from the motor pistons were subjected to fatigue tests at ambient temperature and at 250°C, 300°C and 350°C. The increase in temperature in each case reduced the fatigue resistance [3]. In papers [4, 5], experiments concerning the influence of pore size on the fatigue strength of Al-Si alloy castings were described. Research has shown that cracks during the fatigue tests were the result of the presence of pores in the material that generated stresses in their surroundings, which is the main cause of fatigue failure [4, 5]. In turn, Maruna et al. [6] determined the fatigue strength of Al-Si-Cu-Mg alloy samples, on which V- shaped surface cuts with different rounding radii (2 mm, 1 mm, 0.3 mm and 0.1 mm) were made. It was found that in the case of cuts with a radius of less than 0.3 mm, the de-cohesion process initiated stress fields forming around the incisions, whereas in other cases, the low fatigue resistance was due to the presence of gas and shrinkage pores in the material [6]. Methodology of own research The AlSi11 alloy batch in the form of chips (fig. 1a) was prepared from the rolling ingot on a TUM 35 lathe without the use of a cooling agent. The chips were cold pressed under the pressure of 30 t to form 10 mm high and 38 mm diameter samples (fig. 1b). a) b) Fig. 1. AlSi11 alloy batch material in the for of chips (a) and pressed sample (b) The package of seven moldings was then pressed in a coincidence manner at 400°C with a processing rate of λ = 25 at an extrusion speed of 4 mm/s. For comparative purposes, a bar of solid ingot was also pressed. The bars produced were 8 mm in diameter. A 1-axis stretch test at ambient temperature according to EN ISO 6892-1 was performed on a Zwick/Roell Z050 strength machine. Fatigue tests were carried out on the MTS 880 endurance machine. During the test, circular samples were subjected to cyclical loads, providing a 1- axial tensile stress (sinusoidal, pulsating). The test was conducted at 10 Hz frequency and the maximum cycle * Dr inż. Łukasz Wzorek (lukasz.wzorek@agh.edu.pl), mgr inż. Mate- usz Wędrychowicz (mateusz.wedrychowicz@agh.edu.pl), dr inż. Tomasz Skrzekut (skrzekut@agh.edu.pl), mgr inż. Piotr Noga (pino- ga@agh.edu.pl), mgr inż. Marcel Wiewióra (marcelw@agh.edu.pl), mgr inż. Mateusz Pacek (mateuszpacek21@interia.pl) – Wydział Metali Nieżelaznych AGH w Krakowie