This paper discusses the feasibility of characterization of graphite morphology and size in flake graphite cast irons based on electromagnetic nondestructive methods. Several flake graphite cast iron specimens whose graphite form and size are different variously were prepared, and their electromagnetic properties such as conductivity and relative permeability were evaluated systematically. The results showed that both conductivity and relative permeability depend mainly on the form and size of graphite. Especially, the conductivity has a good correlation with form and size of graphite independently from the pearlite ratio of matrix. The conductivity was found to be correlated highly with ultrasonic velocity, and the ultrasonic velocity was found to be highly correlated with amount and size of graphite. Therefore, measurement of conductivity and permeability can be considered to be well applicable to evaluate form and size of graphite in flake graphite cast irons. Focusing on the fact, DC potential drop method was applied to evaluation of graphite form and its capability was evaluated.

抄録全体を表示

  The feasibility of fabricating butt joints made of dissimilar materials thixomolded magnesium alloy AZ91D and titanium, by friction stir welding method (FSW) was studied. AZ91D and titanium plates of 2mm in thickness were butt-joined FSW according to different joining parameters for probe position and axial tool loads. A probe was inserted at the AZ91D side and the probe edge was slightly offset from the joint interface into the titanium side by up to 0.5mm. AZ91D plates were positioned at the advancing side and the titanium was positioned at the retreating side, respectively.
  The tensile strength of the joint increased with increasing probe distance from the joint interface into the titanium side. Maximum tensile strength reached 226MPa at axial tool load of 7.8kN and probe position of 0.5mm into the titanium side. The joint efficiency was at least more than 95%. At the joint interface, intermetallic compound of titanium and aluminum was not found under a scanning electron microscope, but a rich aluminum layer was seen formed near the interface of the AZ91D and titanium.

抄録全体を表示

  Thin wall ductile cast iron has many graphite nodules about 1000 counts/mm² or more. Fracture toughness of cast iron is affected by graphite nodule counts. But it cannot be evaluated by usual testing because of its small thickness. The small punch test is a method which allows mechanical properties to be determined by small thickness specimens. Evaluation of fracture toughness was carried out using this test. The matrix of specimens was changed to 0 to 80% pearlite by heat treatment. Thin wall ductile cast iron with 50% pearlite or less showed lower fracture toughness than thick wall ductile cast iron, while the fracture toughness was the same for both cases having 50% pearlite or more. As a result of investigating the effects of nodule counts on fracture toughness in ductile cast iron with ferrite matrix, the fracture toughness was found to decrease with increasing nodule count until 600 counts/mm², but remained nearly constant over 600 counts/mm².

抄録全体を表示

  Upset welding of spheroidal graphite cast iron to three kinds of stainless steel (SUS430, SUS304, SUS310) was carried out under various welding conditions. The specimen was 10mm in diameter and 100mm in length. Microstructure observation was employed in order to clarify the characteristics of the bonding interface. Vickers hardness, tensile strength, and elongation of the welded specimen were investigated. FCD previously occurred to the melt of the base metal on the bonding interface than SUS. In the upset welding, the melted part on the welded specimen was exhausted to the edge side, and the part changed into a mottle structure. The microstructure of the welded specimen changed into a spheroidal graphite cast iron structure in pearlite matrix from the mottled structure with increasing heat input. Carbidi precipitation of about 10 to 25μm in size was observed on the SUS side bonding interface.

抄録全体を表示

  In the die casting process, it is important to stabilize depriving die of the heat that is more than half solidification energy of die castings. This study examined influences of cooling functions inside a die with controlled water quality and cooling conditions. The results clarified surface phenomena of the cooling channels inside the die and showed the basic idea for maintaining stability of the water channels inside the die.
  The surface of the cooling channels inside the die changed in various ways according to cooling conditions such as presence of scale and rust, changing physical properties of die material due to corrosion, surface roughness, whether water was drained out or not during cooling inside the die. Stabilizing the surface of the cooling channels inside the die was found to require non-scale water quality to prevent rust corrosion in the water and atmospheric corrosion.

抄録全体を表示