Microstructural Dependence on Fracture Resistance in 7000 Series Aluminium Alloys.
ABSTRACT
The primary aim of this paper is to study the Microstructual influence on fracture resistance in 7000 seriers aluminium alloys. Fracture toughness is an indication of the resistance of a material to physical separation by a process of unstable macrocrack propagation. The microstructural features such as coarse particles of intermetallic (IM) phases, dispersoids, inter- and intragranular precipitates, precipitate-free zones , grain size and orientation are known to exert significant effects on fracture resistance.So this paper focusses on the above microstructural parameters which affect the fracture resistance and models explaining the relationship between these parameters and fracture resistance.
I. Introduction
In general 7000 aluminium alloys have a complex microstructure, which typically consists of coarse intermetallic (IM) particles with sizes in the range of 1 to 20 μm which break easily, intermediate Cr-, Mn- or Zr- rich dispersoids having 0.05- to 0.5- μm average size, relatively coarse quench-induced precipitates and fine strengthening precipitates being smaller than 0.02 μm that strengthen the matrix. The microstructural heterogenities mainly associated with the existence of differently sized second-phase particles plays very important role in triggering the fracture process and then in determining the fracture toughness level[1,8]. These heterogeneities can contribute both to the localisation of plastic flow, and to the initiation and propagation of failure. The toughness in aluminium alloys can be equated with the resistance to crack extension by the ductile or fibrous mode, and this involves the growth and linking-up of voids nucleated by the cracking or decohesion of second phase particles[3]. Consequently the important metallurgical factors are connected with : 1) the distribution of the particles that crack, 2) the resistance of the particles and their interfaces to cleavage and decohesion, 3) the local strain concentrations which
The primary aim of this paper is to study the Microstructual influence on fracture resistance in 7000 seriers aluminium alloys. Fracture toughness is an indication of the resistance of a material to physical separation by a process of unstable macrocrack propagation. The microstructural features such as coarse particles of intermetallic (IM) phases, dispersoids, inter- and intragranular precipitates, precipitate-free zones , grain size and orientation are known to exert significant effects on fracture resistance.So this paper focusses on the above microstructural parameters which affect the fracture resistance and models explaining the relationship between these parameters and fracture resistance.
I. Introduction
In general 7000 aluminium alloys have a complex microstructure, which typically consists of coarse intermetallic (IM) particles with sizes in the range of 1 to 20 μm which break easily, intermediate Cr-, Mn- or Zr- rich dispersoids having 0.05- to 0.5- μm average size, relatively coarse quench-induced precipitates and fine strengthening precipitates being smaller than 0.02 μm that strengthen the matrix. The microstructural heterogenities mainly associated with the existence of differently sized second-phase particles plays very important role in triggering the fracture process and then in determining the fracture toughness level[1,8]. These heterogeneities can contribute both to the localisation of plastic flow, and to the initiation and propagation of failure. The toughness in aluminium alloys can be equated with the resistance to crack extension by the ductile or fibrous mode, and this involves the growth and linking-up of voids nucleated by the cracking or decohesion of second phase particles[3]. Consequently the important metallurgical factors are connected with : 1) the distribution of the particles that crack, 2) the resistance of the particles and their interfaces to cleavage and decohesion, 3) the local strain concentrations which