The Study of Fracture Behaviour of Recycled Aluminium Alloys
from Automotive Component
M.N. Mazlee
School of Materials Engineering
Universiti Malaysia Perlis (UNIMAP)
Jejawi, 02600 Arau, Perlis
Malaysia
mazlee@unimap.edu.my
ABSTRACT
The research has been carried out using recycled petrol (denoted as Alloy A) and diesel (denoted as Alloy B) aluminium engine blocks respectively. The specimens have been fabricated via sand casting process. Two specimens have been chosen were 100 wt. % Alloy B (specimen W) and 30 wt. % Alloy A : 70 wt. % Alloy B (specimen Z). Both specimens have fractured by tensile test. The fracture surface was studied using scanning electron microscope in order to characterise the fracture behaviour of the alloys. It was found that specimen W showed the ductile behaviour which exhibited void formations, dimples and shear fractures whereas specimen Z showed the brittle behaviour such as cleavage fractures.
Keywords: aluminium engine block, sand casting, tensile strength, ductile behaviour, brittle behaviour.
INTRODUCTION
Aluminium has been recycled since the days it was first commercially produced and today recycled aluminium accounts for one-third of global aluminium consumption worldwide. Recycling is an essential process of the aluminium industry and makes sense economically, technically and ecologically. The recycling of aluminium requires only 5 percent of the energy to produce secondary metal as compared to primary metal and generates only 5 percent of the green house emissions (1,2).
It is possible to recycle aluminium alloys based on automotive component. In our research, the diesel and petrol engine blocks have been taken as recycled aluminium. In addition, there is no systematic investigation of fracture mechanism on recycled engine component of aluminium.
Fracture mechanism of aluminium alloy is a very important study in determining the behaviour of that material under applied loads. Therefore, this paper presents the fracture mechanism of recycled aluminium alloys from automotive component.
EXPERIMENTAL PROCEDURE
The recycled petrol (denoted as Alloy A) and diesel (denoted as Alloy B) aluminium engine blocks have been used for remelting process. Two alloys W and Z were taken from diesel and petrol engine blocks. Both alloys were mixed according to the weight percent (wt. %) i.e 100 wt. % Alloy B (specimen W) and 30 wt. % Alloy A : 70 wt. % Alloy B (specimen Z). The mixture is remelted in oil fired furnace and cast into the sand mould. The cast specimens were machined according to the ASTM Standard E557 for tensile test. The micrographs of fractured surfaces were captured and analysed by using a scanning electron microscope (Leica Cambridge S360 model).
RESULTS AND DISCUSSION
Referring to the Figure 1, it shows small and shallow dimples morphology, less plastic deformations in the matrix, intermetallic inclusions (white coloured phase) form linkages network and decohesion phenomenon at the matrix alloy on the surface of specimen W alloy. It also shows small void associated with small dimples (marked by triangular line) and shear mode fracture (marked by black rounded line). The involvement of inclusions in the crack extension process is made evident by their presence within the voids which give the fracture surfaces the characteristic ‘dimpled’ appearance (3). Figures 3 and 5 show fracture surfaces of specimen W at 500 x and 2000 x magnification respectively. In Figure 3, it clearly shows the shear mode fracture (marked by black rounded line) besides linkages of intermetallic inclusions. Meanwhile, Figure 5 shows void formation and coalescence surrounding by linkages of intermetallic inclusions.
However, in contrast observed that many cleavages at matrix alloy and ‘semi’ shear fractures have appeared in Figure 2. In general, Figure 2 shows a brittle morphology. It was also observed that a small crack (marked by SC) also appeared in between the intermetallic inclusions. A same cleavage with large size around 100 mm has been identified and being marked in Figure 2 and Figure 4 by white rounded line. Figure 6 shows a multi layer cleavage surfaces. The cleavage surfaces appear somehow that fracture happens at preferential slip plane.
Based on the appearances, it shows that the ductile fracture has taken place in specimen W meanwhile brittle fracture had been happened in specimen Z. In monolithic metals, ductile fracture follows the sequence of void nucleation, void growth and void coalescence (4,5). Intermetallic inclusions (white coloured phase) between the dimples and cleavage surfaces in specimen Z will decrease the cohesiveness bonding in the matrix thus tensile strength property will be weaken further.
M.N. Mazlee
School of Materials Engineering
Universiti Malaysia Perlis (UNIMAP)
Jejawi, 02600 Arau, Perlis
Malaysia
mazlee@unimap.edu.my
ABSTRACT
The research has been carried out using recycled petrol (denoted as Alloy A) and diesel (denoted as Alloy B) aluminium engine blocks respectively. The specimens have been fabricated via sand casting process. Two specimens have been chosen were 100 wt. % Alloy B (specimen W) and 30 wt. % Alloy A : 70 wt. % Alloy B (specimen Z). Both specimens have fractured by tensile test. The fracture surface was studied using scanning electron microscope in order to characterise the fracture behaviour of the alloys. It was found that specimen W showed the ductile behaviour which exhibited void formations, dimples and shear fractures whereas specimen Z showed the brittle behaviour such as cleavage fractures.
Keywords: aluminium engine block, sand casting, tensile strength, ductile behaviour, brittle behaviour.
INTRODUCTION
Aluminium has been recycled since the days it was first commercially produced and today recycled aluminium accounts for one-third of global aluminium consumption worldwide. Recycling is an essential process of the aluminium industry and makes sense economically, technically and ecologically. The recycling of aluminium requires only 5 percent of the energy to produce secondary metal as compared to primary metal and generates only 5 percent of the green house emissions (1,2).
It is possible to recycle aluminium alloys based on automotive component. In our research, the diesel and petrol engine blocks have been taken as recycled aluminium. In addition, there is no systematic investigation of fracture mechanism on recycled engine component of aluminium.
Fracture mechanism of aluminium alloy is a very important study in determining the behaviour of that material under applied loads. Therefore, this paper presents the fracture mechanism of recycled aluminium alloys from automotive component.
EXPERIMENTAL PROCEDURE
The recycled petrol (denoted as Alloy A) and diesel (denoted as Alloy B) aluminium engine blocks have been used for remelting process. Two alloys W and Z were taken from diesel and petrol engine blocks. Both alloys were mixed according to the weight percent (wt. %) i.e 100 wt. % Alloy B (specimen W) and 30 wt. % Alloy A : 70 wt. % Alloy B (specimen Z). The mixture is remelted in oil fired furnace and cast into the sand mould. The cast specimens were machined according to the ASTM Standard E557 for tensile test. The micrographs of fractured surfaces were captured and analysed by using a scanning electron microscope (Leica Cambridge S360 model).
RESULTS AND DISCUSSION
Referring to the Figure 1, it shows small and shallow dimples morphology, less plastic deformations in the matrix, intermetallic inclusions (white coloured phase) form linkages network and decohesion phenomenon at the matrix alloy on the surface of specimen W alloy. It also shows small void associated with small dimples (marked by triangular line) and shear mode fracture (marked by black rounded line). The involvement of inclusions in the crack extension process is made evident by their presence within the voids which give the fracture surfaces the characteristic ‘dimpled’ appearance (3). Figures 3 and 5 show fracture surfaces of specimen W at 500 x and 2000 x magnification respectively. In Figure 3, it clearly shows the shear mode fracture (marked by black rounded line) besides linkages of intermetallic inclusions. Meanwhile, Figure 5 shows void formation and coalescence surrounding by linkages of intermetallic inclusions.
However, in contrast observed that many cleavages at matrix alloy and ‘semi’ shear fractures have appeared in Figure 2. In general, Figure 2 shows a brittle morphology. It was also observed that a small crack (marked by SC) also appeared in between the intermetallic inclusions. A same cleavage with large size around 100 mm has been identified and being marked in Figure 2 and Figure 4 by white rounded line. Figure 6 shows a multi layer cleavage surfaces. The cleavage surfaces appear somehow that fracture happens at preferential slip plane.
Based on the appearances, it shows that the ductile fracture has taken place in specimen W meanwhile brittle fracture had been happened in specimen Z. In monolithic metals, ductile fracture follows the sequence of void nucleation, void growth and void coalescence (4,5). Intermetallic inclusions (white coloured phase) between the dimples and cleavage surfaces in specimen Z will decrease the cohesiveness bonding in the matrix thus tensile strength property will be weaken further.
CONCLUSIONS
1) The ductile behaviour of remelted aluminium alloys showed the appearance of void formations, dimples and shear fractures.
2) The brittle behaviour of remelted aluminium alloys showed the appearance of cleavage fractures.
REFERENCES
1) http:/www.world-aluminium.org/production/recycling/index.html, Aluminium the Material.
2) Mazlee Mohd. Noor, (2003), Aluminium Kitar Semula; Perspektif Sektor Pengangkutan, Dewan Kosmik, Karangkraf Sdn. Bhd.
3) Derby, B., (1995), Microstructure and Fracture Behaviour of Particle-Reinforced Metal-Matrix Composites, Journal of Microscopy, 177, 357-368.
4) Hahn, G.T. & Rosenfield, A.R., (1975), Metallurgical Factors Affecting Fracture Toughness of Aluminium Alloys, Metall. Trans. A, 6(A), 653-683.
5) Shivkumar, S., Wang, L. & Apelian, D., (1991), Molten Metal Processing of Advanced Cast Aluminium Alloys, Journal of the Minerals, Metals and Materials Society, 43, 26-32.
No comments:
Post a Comment