Fracture and Fatigue Behaviour of Aluminium Matrix Composite Automotive Pistons
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Fracture and Fatigue Behaviour of Aluminium Matrix Composite Automotive Pistons Ane M. García-Romero & Pedro Egizabal & Angel M. Irisarri
Received: 17 July 2009 / Accepted: 9 November 2009 / Published online: 28 November 2009 # Springer Science + Business Media B.V. 2009
Abstract The fracture and fatigue behaviour of prototype automotive pistons produced in an aluminium alloy matrix composite in industrial conditions has been studied. Fracture toughness increased when the testing temperature rose from 20° to 75°C and kept near constant up to 250°C, when a significantly lower value was recorded. A change in the failure operating mechanism, which can explain this trend, was observed by analysing the fracture surfaces in the scanning electron microscope. Room temperature fatigue tests performed with R=0.1 stress ratio led to an average value of the Paris law exponent higher than those reported in aluminium alloys but low for an industrially produced brittle composite. A higher exponent and a much larger scattering were observed in those fatigue tests carried out under R=0.5 stress ratio. Keywords Aluminium matrix composite . Prototype piston . Fracture . Fatigue
1 Introduction Automotive pistons are usually made of a specific alloy, worldwide known as the “piston alloy”. This alloy is composed of a eutectic aluminium–silicon matrix (12%Si), containing also 1% Ni, 1% Cu, 1% Mg, and a small percentage of iron which constitutes the main impurity of the alloy. Reasons for choosing this alloy must be found in its high wear and corrosion resistance, together with a well determined thermal expansion coefficient and having toughness high enough for the intended application. Automotive pistons are worldwide produced by the squeeze casting process because this is a near net shape process with good production rate at a reasonable price, prime requirements in this sector.
A. M. García-Romero Departamento Ingeniería Minera, Metalurgia y Ciencia de los Materiales, Escuela Universitaria de Ingeniería Técnica de Minas y de Obras Públicas. EHU-UPV, Barakaldo, Spain P. Egizabal (*) : A. M. Irisarri INASMET—Tecnalia. Automotive Unit, Mikeletegi Pasealekua 2, 20009 San Sebastian, Spain e-mail: [email protected]
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Appl Compos Mater (2010) 17:15–30
Metal matrix composites are complex materials constituted by a certain volume fraction of continuous or discontinuous ceramic reinforcement fibres or particles inserted in the metallic alloy matrix. Reasons for using metal matrix composites in the automotive industry in general, and in the case of the pistons in particular, must be found in the increased specific stiffness, the excellent wear resistance, prime considerations for these components, and the improved high cycle fatigue behaviour [1]. Drawbacks of composite materials are linked to a reduction of toughness, compared to the matrix alloy, changes in the thermal behaviour, and higher heterogeneity. In addition, their higher cost usually constitutes the main drawback for the industrial implementation of these materials. However,
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