Rupture of intermetallic networks and strain localization in cast AlSi12Ni alloy: 2D and 3D characterization

A Tireira,G Requena,S Sao Jao,A Borbely,H Klocker

doi:10.1016/j.actamat.2016.04.020

A Tireira, G Requena + Show 3 more

Open Access

https://doi.org/10.1016/j.actamat.2016.04.020

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Abstract

Damage development during tensile straining of a cast AlSi12Ni alloy has been characterized by in situ SEM imaging and synchrotron X-ray microtomography. Two main damage mechanisms consisting of intermetallic particle rupture and decohesion of Al-Si interfaces were revealed. Particle rupture takes place already from the beginning of the deformation, while decohesion of Al-Si interfaces is more characteristic at later stages. It is shown that damage evolution in the alloy is closely related to the underlying geometry of the intermetallic phase, its clustered structure playing a double role in controlling strain localization in the matrix as well as the rupture sequence of the intermetallic phase itself. The latter shows that small clusters break-off from the complex intermetallic network before large clusters, in good agreement with their load carrying capacity determined by the local volume fraction of the intermetallic phase. Finite element modeling of the alloy's tensile behavior evidences that deformation bands formed in the alloy with complex structure are similar to those developed in a model particle reinforced metal-matrix composite, where the particles correspond to the clustered regions of the intermetallic phase.

Highlights

Cast Al-Si alloys are widely used in the automotive industry for cylinder heads, pistons and engine crankcases due to their excellent castability as well as lower weight and better heat transfer compared to cast iron
It is well known that strain localization and damage are strongly interrelated, it is less known how are they influenced by the geometrical characteristics of the underlying structure
Damage development during tensile straining of a cast AlSi12Ni alloy has been characterized in situ by Scanning Electron Microscopy (SEM) imaging and synchrotron X-ray micro-tomography

Summary

Introduction

Cast Al-Si alloys are widely used in the automotive industry for cylinder heads, pistons and engine crankcases due to their excellent castability as well as lower weight and better heat transfer compared to cast iron. Three dimensional (3D) interconnected networks of brittle intermetallic (IM) phases can form depending on the chemical composition of the alloy (e.g. Al9FeNi and Al15Si2(FeMn)3) [5] These networks are usually connected to the eutectic and the primary Si leading to a rigid and highly interpenetrating structure. It is well known that strain localization and damage are strongly interrelated, it is less known how are they influenced by the geometrical characteristics of the underlying structure (for instance by the geometry of the hard phase, which in the present case is represented by the network of rigid phases) It is the aim of the present work to explore this connection through two distinct characterization techniques. Finite Element Modeling (FEM) of the plastic behavior of the alloy with highly complex structure allows gaining insight into the role played by the hard IM phases on strain localization

Material and microstructure

Particle tracking algorithm

Break-up sequence of a large intermetallic particle

Geometrical analysis of the complex IM structure

Finite element modeling of the mechanical behavior

Conclusions