Number Of Si Particles Research Articles

3D connectivity of eutectic Si as a key property defining strength of Al–Si alloys

The relationship between microstructure and mechanical behavior of the eutectic phase in hypoeutectic Al–Si alloys is analyzed empirically using two experimental and thirteen synthetic microstructures. For all microstructures, a morphological analysis is combined with mechanical stress–strain simulations performed via finite element method (FEM). The synthetic microstructures are generated by a stochastic microstructure model that gives a realistic description of the eutectic Si in Al–Si alloys. The stochastic model was developed on the basis of a 3D image of a real Sr-modified Al–Si alloy and is used to generate a large variety of virtual 3D structures of eutectic Si that differ from each other by the number of Si particles, their degree of branching, and connectivity. In the simulation study, it is shown that highly connected and branched morphologies of Si are beneficial to the strength of the material. Besides, when the connectivity of Si is low, i.e. when an Al matrix is reinforced by discrete (disconnected) particles of Si, the strength of the material increases with the number of those particles. The Euler number is shown to be highly effective in characterizing the connectivity and is closely related to the strength of the material.

Mechanical testing of titanium/aluminium–silicon interface: Effect of T6 heat treatment

A previous paper reported on the mechanical behaviour of insert-moulded Ti/Al–7Si bimetallic test pieces as studied by a classical push-out test as well as a variant: the circular bending test. When a chemical bond was formed at the Ti/Al–7Si interface, promising results were obtained in terms of joint strength and damage mechanism (Dezellus et al., 2008 [1]). As a continuation, the aim of the present work was to examine the influence on this mechanical behaviour of a T6 heat treatment (re-heating for 10h at 540°C, quenching in cold water and ageing for 6h at 170°C) applied to the as-moulded Ti/Al–7Si test pieces. For that purpose, push-out and circular bending tests were performed on heat-treated samples, and the results were correlated with a characterization of the morphology, the constitution and composition of both transverse sections through the metal/metal reaction zone and fracture surfaces, as revealed after removal of the Ti insert. As expected, applying the T6 heat treatment to chemically bonded Ti/Al–7Si bimetallic assemblies resulted in an improvement of the mechanical properties of the Al–7Si matrix itself. Moreover, a significant increase of the load level for the onset of joint damage in push-out mode was observed. Concerning the damage mechanism, the presence of angular Si particles in the eutectic region of the Al–7Si matrix near the interface had a weakening effect. After T6 solution heat-treatment, the shape of the Si particles changed from angular to globular. Moreover, due to the formation of Si-rich compounds at the Al–7Si/Ti interface, Si diffuses from the alloy towards the Ti rod and the size and number of Si particles became significantly decreased near the insert/alloy interface. These two features explained the favourable influence of the T6 heat-treatment on the mechanical properties of the Ti/Al–7Si assemblies.