Optimization of the Heat Treatment and Tribological Properties of 2024 and 7075 Aluminium Alloys

Abstract

This paper describes two stages of optimization of the properties of 2024 and 7075 aluminium alloys, in particular their resistance to pitting by first T6, T6I6 or T6I4 treatment, and second increase its tribological properties by depositing by RF PACVD method a gradient coating of high adhesion to the substrate.Quantitative microstructural characteristics reveals that it is possible to increase hardness (up to 190HV for 7075 alloy) with relatively high yield strength (520 MPa) and high ultimate elongation (about 20%) by optimizing dispersion of precipitates using two-stage artificial aging process.Next to eliminate forming of thin Al 2 O 3 layer with relatively poor adhesion to the aluminium substrate, gradient a-C: H/Ti layers synthesis hybrid plasma chemical RF PACVD reactor equipped with pulsed magnetron sputtering system was used. Using such configuration enables forming a thick and highly adherent diamond-like carbon layer on aluminium surface with low coefficient of friction (0.05), at a substrate temperature below 470K. Due to application of Ti magnetron cathode it was possible to improve the adhesion strength up to 30mN of diamond-like carbon layer to the covered substrate. Influence of deposition parameters on microhardness profile as well as adhesion and morphology were determined by nanotest and AFM, respectively.Keywords: aluminium alloy, heat treatment, coating, coefficient of friction W niniejszym artykule przedstawiono wyniki badań doboru parametrów dwuetapowego procesu obróbki cieplnej stopów aluminium, w szczególności podwyższenia odporności na pitting poprzez zastosowanie obróbki T6, T6I4 lub T6I6 oraz odporności na zacieranie poprzez osadzenie metodą RF PACVD warstw gradientowych o wysokiej adhezji do podłoża.Przeprowadzona analiza wyników badań dowodzi, że istnieje możliwość podwyższenia twardości (nawet do 190 HV dla stopu 7075) przy relatywnie wysokiej jego granicy plastyczności (520 MPa) i wysokim wydłużeniu przy zerwaniu (20%) na drodze optymalizacji dyspersji wydzieleń poprzez zastosowanie dwuetapowego starzenia.W celu wyeliminowania tworzenia się cienkiej warstwy Al 2 O 3 charakteryzującej się relatywnie niska adhezją do podłoża osadzono, przy pomocy reaktora RF PACVD wyposażonego w źródło rozpylania magnetronowego, gradientową powłokę a-C: H/Ti. Zastosowanie niniejszej konfiguracji umożliwiło w temperaturze poniżej 470K wytworzenie na podłożu aluminiowym cienkiej, dobrze przylegającej powłoki węglowej charakteryzującej się niskim współczynnikiem tarcia (0.05). Zastosowanie tytanowej katody magnetronowej umożliwiło osiągnięcie wartości adhezji powłoki węglowej do podłoża na poziomie 30 mN.Wpływ parametrów osadzania zarówno na profil mikrotwardości jak i adhezję oraz morfologię przebadano przy użyciu technik nanoindentacji oraz Mikroskopu Sił Atomowych.

Influence of gas mixture during N+ ion modification under plasma conditions on surface structure and mechanical properties of Al–Zn alloys

“…The experiment was conducted to facilitate the modification of alloy surface in the reactor, concurrently being the second stage of the aging process. For that reason, temperature parameters as well as the time of plasmochemical processing were selected based on the optimum conditions from secretion processes of the mentioned alloys [15].…”

“…Additionally, documented investigations [11][12][13][14] prove that the most promising aluminum alloys aimed for the elements exposed to high load and wear are, inter alia, the alloys of 2xxx and 7xxx series. However, there is a significant limitation of the mentioned materials' application, related to their low resistance to scuffing and contact fatigue [15].…”

“…physical vapor deposition (PVD) [16], plasma assisted chemical vapor deposition (PA CVD) [17], ion implantation [18], and pulse laser deposition (PLD) [19][20][21][22], are used in order to improve the utility value of the surfaces. Taking into account the discussed alloys, PA CVD technology enabling considerable lowering of the temperature processes conducted in the reactor [15,23,24] is a promising method. This application method allows avoidance of the unprofitable process of aluminum alloy overaging which, as a consequence, leads to grain growth and precipitation coagulation, causing deterioration of the substrate mechanical properties, including resistance on contact fatigue [9].…”

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“…Recently, in order to achieve this purpose, a number of conventional methods have been applied, including microstructure optimization during heat treatment processes, shoot penning, surface engineering, etc. [ 1 , 2 ]. Compared with traditional aluminum alloys, aluminum–lithium alloys have higher specific strength, higher specific stiffness, better heat stability and corrosion resistance, which can significantly improve the properties of aircraft and extend their service life.…”

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“…So the trend is to Received: 2017 replace the heavy parts with some another material such as light alloys [7,14]. The problem with these alloys is their poor mechanical properties.…”