Tear Toughness of Permanent Mold Cast and DC Cast A356 Aluminum Alloys

Abstract

Cast products of A356 with different microstructural features were prepared; permanent-mold cast (PM) and direct-chill cast (DC) products. For each casting, a sharp notched plate specimen was subjected to static tensile loading until a crack initiated at the notch root and propagated across the width of the specimen. Both maximum load and energy to fracture (the integrated area under the load-displacement curve) increased with decreasing dendrite arm spacing (DAS). The curve of DC was smooth and the energy to fracture was quite large. The loaddisplacement curve was divided into two segments by a vertical line through the maximum load. The area under the first segment is a measure of the energy necessary to initiate the crack. The second segment represents the energy necessary for crack propagation. Unit energy was computed by dividing the measured energy by the net area of the specimen. Refinement of DAS and grain size increased unit energies for crack initiation (UEi) and propagation (UEp). Comparison among PM products revealed that DAS refinement was effective for increasing UEi. Among the present castings, the DC product with the finest DAS exhibited a significant increase in UEp. Observation of the crack propagation path revealed that the fracture surface was normal to the loading direction for PM. In contrast, for DC, a slanted crack path was dominant through the specimen ligament. The features of the crack propagation path are considered to have affected quantitative balance between UEi and UEp. The increased UEp in DC is considered to be due to the introduced slanted crack. Tear tests were confirmed to provide useful information concerning the effect of solidification structure on toughness, which can serve as a guide for further toughening of aluminum alloy castings.

Tear Toughness Evaluation of a Permanent Mold Cast A356 Aluminum Alloy Using a Small-size Specimen

“…Recently, Kumai et al 8) examined the effect of solidification structure on tear toughness for several permanent mold cast (PM) and direct-chill cast (DC) products of the A356 aluminum alloy. Refinement of DAS and grain size increased both UEi and UEp.…”

“…Han et al examined tear toughness of permanentmold cast and semi-liquid die-cast A356 aluminum alloys. 7) Recently, Kumai et al 8) performed tear tests for permanentmold cast and direct-chill cast A356 aluminum alloys, and investigated the effect of solidification structure on both unit crack initiation energy (UEi) and UEp. Fine dendrite arm spacing was revealed to be effective for increase in UEp.…”

Effect of Cooling Rates during Solidification of Al-5.5%Mg-2.3%Si-0.6%Mn and Al-13%Mg<SUB>2</SUB>Si Pseudo-Binary Alloys on Their Secondary-Particle Morphology and Tear Toughness

“…In this case, the effect of metallurgical microstructure is masked even though the refined microstructure is beneficial for increase in ductility. In contrast, a series of previous works by Kumai et al [2][3][4][6][7][8][9] found that the loaddisplacement curve obtained by the tear test using a notched specimen shows good reproducibility even if casting defects are included in the specimen. In addition, they reported that the shape of load-displacement curve is quite sensitive to the microstructural change of the specimen.…”

“…1,2) Not only wrought aluminum alloys such as 5000 and 6000 series alloys but also AC4CH cast alloys and ADC12 die-cast alloys were cast into thin plates and their solidified structure and mechanical properties were investigated. [2][3][4] This casting method is applicable to obtain the rapidly solidified specimens in the present study.…”

“…5) Kumai et al [2][3][4][6][7][8][9] have employed the tear test to examine the relationship between solidification structure and tear resistance. Tensile test using a smooth bar or a plate specimen is a standard method for mechanical property evaluation.…”