The objective of this study is to investigate the effects of Maganese (Mn) on continuous cooling transformation behavior and heat treatment characteristics of low alloyed shperoidal graphite cast iron containing 0.5 to 3mass%Mn. Austenitizing was performed at 1223K and 900s, and the cooling time from Ac₃ to 773K was varied about 3 to 4000s. All of the ferritic, pearlitic, bainitic and martensitic transformations were observed for small (0.5%) Mn content. On the other hand, ferritic transformation did not occur when Mn was more than 3mass% and the bainitic one never when more than 1.5%. This was due to the fact that manganese inhibited the precipitation of ferrite for bainite nucleus. Manganese lowers A₃ temperature and increases carbon content in the matrix, thereby lowering Ms temperature. As the C content in the matrix was consumed for graphite or cementite growth at a cooling time of more than 100s, the Ms temperature tended to elevate. Gross residual austenitic structures appeared in quenched microstructures of 1.5 and 3%Mn cast irons. As higher Mn content and shorter cooling time produces larger austenites, the formation of these gross resudual austenite structures is considered to be induced by the drop in Ms temperature. The amount of residual austenites decreased when the cooling time was more than 100s and the amount of martensites decreased when 500s in 1.5 and 3%Mn cast iron. The hardening curve was therefore convex at cooling time ranges of 40 to 70s or 100 to 500s. The hardenability of the cast irons improved by increasing the Mn content.

抄録全体を表示

  A twin roll caster of vertical type with 1500 diameter rolls was designed and assembled to cast an aluminum alloy strip. Strip casting of 6016 (0.16%Fe) and impurity -Fe added 6016 (0.45%Fe) was attempted using this caster. Both 6016 (0.16%Fe) and 6016 (0.45%Fe) could be cast into the strip continuously at the speed of 60m/min. Use of copper rolls and non-use of lubricant contributed to improvement of the cooling rate and casting speed of the strip. The thickness of the strip was 3.4mm. The microstructure was very fine. The as-cast strip could be cold-rolled without homogenization down to 1mm. The T4-heat treated strip of 6016 (0.16%Fe) and A6016 (0.45%Fe) could be bent 180 degrees without breaking. There was no influence of Fe content on bending-ability. Bending-ability of the strip was improved by rapid solidification of the twin roll caster in the present study. The twin roll caster in the present study was useful for decreasing the influence of impurity Fe.

抄録全体を表示

  In order to simplify the manufacturing process of complex structured slide-bearings used at the large ends of connecting rods in automotive engines, direct coating of bearing material mainly by thermal spraying is being examined. Newly substituted lead-free metals like aluminum-based alloys are appealing as slide-bearing material candidate. Hot-dip coatings practically employed in the manufacturing of zinc alloy coated steel sheets. However, it is difficult to coat aluminum alloy on bulky steel substrates without sufficient preheating, because a rapidly solidified layer containing gas babbles is formed on a substrate surface. A variety of iron-aluminides are also formed at the interface of steel and aluminum hot-dip coatings, which is the main reason for the difficulty in joining steel with aluminum.
  Ultrasonic vibration was applied to a steel substrate during the hot-dip coating of aluminum alloy to suppress the rapidly solidified layer and a brittle reaction layer. Hot dipping of columnar steel substrates into molten aluminum alloy (Al-2.7mass%Si-4.6mass%Sn) was carried out through the use of a Langevin oscillator with a resonant frequency of 19.5kHz. The application of ultrasonic vibration is quite effective for removing rapidly solidified layers and surface oxide layers from the substrate surface by sonocapillary effects based on the cavitation phenomenon, so that intimate contact is achieved at the beginning of hot-dip coating. When the hot-dipped substrate surface is heated higher than liquid temperature, a brittle intermetallic reaction layer of Fe₂Al₅ grows at the interface. However, the application of ultrasonic vibration to hot-dipping is effective for controlling reaction layers less than 5μm in thickness. Impact test showed good adhesive strength of hot-dipped aluminum coatings with a thin reaction layer of approximately 5μm.

抄録全体を表示

  6061 aluminum alloy and model material of recycled 6061 aluminum alloy with increased Fe were cast into strips at a speed of 0.5m/s using an unequal diameter twin roll caster. The Fe content of 6061 aluminum alloy and the model material of recycled 6061 aluminum alloy was 0.36mass% and 0.59mass%, respectively. Ripple marks, which are typical surface defect of roll cast strips, did not occur on the surface of both as-cast strips. Fe content did not influence the surface condition of the roll-east-strip. The as-cast strip was cold rolled down to 1mm, T4 heat treatment was conducted, and then subjected to π rad (180°) bending test. The result π rad (180°) bending test shows that roll cast 6061 aluminum alloy and 6061 aluminum alloy with increased Fe as recycled material had the same bending ability as that of roll-cast 6022 aluminum alloy. In the strip casting by the twin roll caster of the present study, increased Fe content did not influence the results of the π rad (180°) bending test.

抄録全体を表示