Fatigue crack growth behavior in semi-liquid die-cast Al-7%Si-0.4%Mg alloys with fine effective grain structure

Han, Sang-Won; Kumai, Shinji; Sato, Akira

doi:10.1016/s0921-5093(00)01981-x

Cited by 20 publications

(7 citation statements)

References 8 publications

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“…The PM microstructure has a dendritic primary alpha phase and the SSM microstructure has a globular alpha phase. PM casting generally produces coarser microstructures with grain in the size range of 180 to 1,500 µm [1,6] whereas SSM microstructures are characterized by a grain size in the range of 30 to 200 µm [1,7,8]. It is still not clear how these microstructural features affect the fatigue behaviour of the solidified alloys.…”

Section: Introductionmentioning

confidence: 99%

Propagation of short fatigue cracks in permanent and semi-solid mold 357 aluminum alloy

Brochu¹,

Verreman²,

Ajersch³

et al. 2012

International Journal of Fatigue

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The high cycle fatigue strengths of aluminum-silicon-magnesium 357 alloy prepared by permanent molding and semi-solid molding are compared at stress ratios R = -1 and R = 0.1. Results show that precipitation hardened permanent mold (PM) and semi-solid mold (SSM) materials have fatigue strengths at R = -1 and 10 7 cycles of 82 and 113 MPa respectively while those at R = 0.1 are 47 MPa and 78 MPa respectively. Part of this difference is explained by the fact that the SSM specimens contain fewer and smaller defects than the PM specimens. Defects reduce the duration of the short crack propagation period, which significantly affects the overall specimen fatigue life. A comparative analysis of the long crack behaviour indicates that the PM microstructure is more resistant to the propagation of long cracks than the SSM microstructure because crack closure is more significant. However, the long crack behaviour cannot be used to predict the specimen fatigue life, which mainly consists of short crack propagation. Observation of many short cracks using the replication technique indicates that grain boundaries are the most 2 important microstructural barrier to short crack propagation in these materials. The results also show that crack growth decelerations occur at a crack depth comparable in size to the average grain radius of the materials. The difference in the distance of these important microstructural barriers can explain the fatigue strength difference measured. It is concluded that the average fatigue strength is inversely proportional to the square root of the average grain size.

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Section: Introductionmentioning

confidence: 99%

Propagation of short fatigue cracks in permanent and semi-solid mold 357 aluminum alloy

Brochu¹,

Verreman²,

Ajersch³

et al. 2012

International Journal of Fatigue

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“…The optical micrographs of the anodized specimens show the grain structure. It has been recognized that crystallographic orientation is different between areas of different colour tones 3–5 . The PM series alloys consist of grains including conventional dendrite cells and eutectic Si particles changed by Ti addition or mould temperatures.…”

Section: Resultsmentioning

confidence: 99%

“…It has been recognized that crystallographic orientation is different between areas of different colour tones. [3][4][5] The PM series alloys consist of grains including conventional dendrite cells and eutectic Si particles changed by Ti addition or mould temperatures. On the other hand, the microstructure of SL is characterized by a globular cell structure, whose spacing is measured as a parameter like DAS in the PM series, and eutectic Si particles.…”

Section: Microstructural Observation and Fractographymentioning

confidence: 99%

“…Each colony is considered to be suitable to be called an 'effective grain'. 4,5 The Si particles are coarse compared with those in the PM series alloys because Strantium was not added. The volume fractions of the cast defects and intermetallic particles are ignored in both PM and SL because they are extremely limited.…”

Section: Microstructural Observation and Fractographymentioning

confidence: 99%

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Effects of solidification structure on tear resistance of Al–7% Si–0.4% Mg cast alloys

Han

Kim

Kumai

2004

Fatigue Fract Eng Mat Struct

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A B S T R A C TThe tear resistance behaviour of Al-7% Si-0.4% Mg cast alloys was examined using Kahntype tear test specimens. Tests were performed for two permanent mould casts with an ordinary dendrite structure and a semi-liquid die cast with a globular cell and fine grain structure. The microstructure of the two permanent mould casts was controlled by the cooling rates and the addition of Ti elements. Tear resistance was evaluated by the 'popin' stress, the energies required for crack initiation, UE i and the crack propagation, UE p . Special attention was paid to an effective microstructural parameter for tear resistance improvement. Pop-in, indicating sudden crack extension and arrest, was observed in all specimens. Homogeneous deformation occurs near the notch tip of the semi-liquid die cast, characterized by a refined grain structure. Refinement of the grain size is more effective than that of the dendrite cell size or eutectic Si particle size to increase the energy for crack initiation. Unit propagation energy, UE p , can be converted into a critical stress intensity factor, K c , which in the semi-liquid die cast was improved due to an increased amount of slant or shear fracture surface.

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“…These microstructural features as well as the precipitation state in the matrix have a considerable influence on mechanical properties. [1][2][3][4][5][6][7][8] Many studies have indicated that the refinement and homogenization of the microstructures are effective for achieving good mechanical properties, such as ductility and toughness. 9,10) Severe Plastic Deformation (SPD) processes such as high-pressure torsion (HPT), [11][12][13] accumulative roll bonding (ARB), 14,15) equal-channel angular pressing (ECAP), 16,17) and friction stir processing (FSP) 18,19) have been developed as new solid-state processing techniques for microstructural modification.…”

Section: Introductionmentioning

confidence: 99%

Effect of Eutectic Si Particle Morphology on ECAP Formability and Mechanical Properties of AC4CH Aluminum Casting Alloys

Nakayama

Miyazaki

2011

Mater. Trans.

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AC4CH casting alloys were subjected to the 2-step preheating and the ECAP processing at room temperature. Microstructure change was investigated in terms of size and globularity of the eutectic Si particles and hardness of the primary and the eutectic -Al. The effects of 2-step preheating, ECAP processing and standard T6 heat treatment on the hardness and the tensile properties were also investigated. The results of this study are as follows. The ECAP formability was significantly improved by the optimum 2-step preheating (1st-step preheating at 560 C and 2nd-step preheating at 350 C). More than 12-times ECAP pressing (equivalent strain of about 5.6) could be made without cracking. The hardness distribution in the primary -Al suggested that the accumulated plastic strain during the ECAP processing increased gradually toward the eutectic cell regions. The hardness measurement also showed that the accumulated plastic strain of the eutectic -Al around less-globular Si particles was higher than that around globular Si particles. Concentration of the plastic strain may promote cracking in the eutectic cell regions and deteriorate the ECAP formability. Successive processing by the 2-step preheating, the ECAP processing and the standard T6 heat treatment brought about globularity and homogeneous distribution of the eutectic Si particles. During the tensile deformation, these microstructural features might lead to homogeneous distribution of the plastic strain, suppressions of the cracking of Si particles and the delamination between the Si particle and the matrix. As a result, the 0.2% proof stress and the fracture strain increased about 11% and 47% respectively compared with those of the standard T6 treated sample.

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Fatigue crack growth behavior in semi-liquid die-cast Al-7%Si-0.4%Mg alloys with fine effective grain structure

Cited by 20 publications

References 8 publications

Propagation of short fatigue cracks in permanent and semi-solid mold 357 aluminum alloy

Propagation of short fatigue cracks in permanent and semi-solid mold 357 aluminum alloy

Effects of solidification structure on tear resistance of Al–7% Si–0.4% Mg cast alloys

Effect of Eutectic Si Particle Morphology on ECAP Formability and Mechanical Properties of AC4CH Aluminum Casting Alloys

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