Characterization of Pore Defects and Fatigue Cracks in Die Cast AM60 Using 3D X-ray Computed Tomography
- PDF / 3,053,446 Bytes
- 10 Pages / 593.972 x 792 pts Page_size
- 0 Downloads / 150 Views
NTRODUCTION
MAGNESIUM alloys are attractive to the automotive industry as they are lighter than aluminum in weight and have good castability. The use of magnesium alloy components in new generation light weight vehicles will improve fuel economy. High pressure die casting (HPDC) is cost-effective, producing large volume magnesium casting components in net shape and with complex geometry.[1] However, the inherent porosity of the casting process retards their wider use. The porosity issue is more serious in thick-wall than thin-wall castings;[1] the former offers a cross section with two microstructures, fine-grain pore-free surface microstructure and coarse-grain internal microstructure with pores. Porosity usually involves both gas pores and shrinkage pores. The former result from the gas entrapment during the rapid injection of molten metal into the die cavity while the latter are due to the volumetric contraction of solidified metal and the lack of extra molten metal to refill the die cavity. ZHUOFEI YANG, Graduate Student, is with the Department of Materials Science and Engineering, McMaster University, Hamilton, L8S 4L8, Canada, and also with CanmetMATERIALS, Natural Resources Canada, Hamilton L8P 0A5, Canada. JIDONG KANG, Research Scientist, is with the Department of Natural Resources, CanmetMATERIALS. Contact e-mail: [email protected] DAVID S. WILKINSON, Distinguished University Professor, Provost & Vice President (Academic), is with the Department of Materials Science and Engineering, McMaster University. Published with permission of the Crown in Right of Canada. Manuscript submitted February 6, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS B
The presence of porosity in a magnesium casting impairs its mechanical performance, especially fatigue properties. Several studies of the fatigue properties of AM60 Mg castings have been conducted.[2,3] The scatter of pore size in AM60 die casting was concluded to be the dominant factor resulting in the large scatter of fatigue life in stress-controlled fatigue.[2] In strain-controlled fatigue, the scatter of fatigue life was also found to be large at low strain levels.[3] The size measurements of porosity in 2D on cross sections or fracture surfaces are not accurate since pores are 3D objects. Therefore, a further in-depth study on the effect of porosity on fatigue properties of AM60 HPDC Mg alloy using X-ray computed tomography (XCT) technique to characterize porosity in 3D will better reveal the role of porosity in fatigue behavior. By conducting an interrupted fatigue test and XCT scan on a specimen at intervals, the effect of porosity on both the crack initiation and crack propagation stages can be studied. Even the fracture surfaces after fatigue testing can be 3D determined by XCT to facilitate failure analysis when interpreted by SEM images. Not only the size of porosity will be measured more accurately in 3D, but also the shape and the location. The interaction of fatigue cracks and porosity during fatigue test can also be visualized. XCT has been increasingly used i
Data Loading...
