Four T-shape AC4C alloy castings (a : T without runner, b : T with runner, c : Inverted T without runner, d : Inverted T with runner) were investigated to reveal the effects of sand casting plan on hot-tearing. Linear defect occurred only at the intersection area of the horizontal bar and vertical bar of type b. Microstructure observation, cooling curve analysis, and defect analysis revealed that hot tearing causes the linear defect. The defect was found to occur only when the casting and mold met the following conditions : a) The vertical bar of the T shape locates downward ; b) The solidification rate of the vertical bar of the T shape is slower than that of the horizontal bar ; c) The intersection area of the T shape passes through the eutectic solidification range with a similar cooling rate of the vertical bar, but the area finally cools down before the vertical bar does.

  The effects of Ti-B contents and Sr addition on the solidified structures and hot-tearing of Al-2～6mass%Mg-0～3mass%Si alloys cast in I-beam shaped mold, were investigated by OM and SEM observations. Hot-tearing of 0.01～0.12mass%Ti-0.002～0.024mass%B added alloys was lower compared with Ti-B free alloys. On the other hand, hot-tearing of 0.014mass%Sr added alloys decreased only in Al-6mass%Mg-3mass%Si alloys. As a reason of decreased hot-tearing, the grain size of the I-beam castings became finer, and eutectic Mg₂Si changed it shape from lamellar to fine plates by the addition of a very small amount of Sr. This results in effective delaying at the beginning of hot-tearing.

  Addition of grain refiner Ti-B and eutectic modifier Sr on the hot tearing of T-shape JIS AC4C alloy castings using a sand mold was investigated. With the T-shape, solidification of the vertical bar portion was slower than that of the horizontal bar. The hot tearing took place at the intersection of the horizontal bar and vertical bar even if the alloy included Ti-B. On the other hand, the alloy including Sr above 0.003% did not show hot tearing, but there was evidence of preceding hot tearing at the surface of the T-shape corner. It was demonstrated in the crack-closing process that the addition of Sr enhances interdendritic feeding of the Al-Si eutectic melt after the Al-Si eutectic reaction.

  Time-resolved X-ray imaging was used to directly observe semi-solid deformation of Al-Cu alloys at two global shear strain rates. At the low shear rate of 10^-3 s^-1 and solid fraction of 55%, the liquid was drawn into the expanded spaces between solid particles caused by rearrangement of solid particles during shear. As a result, a shear band with the relatively lower solid fraction was formed. On the other hand, at higher shear rates of 10^-1 s^-1 and solid fraction of 47%, sufficient liquid did not flow into the expanding spaces, resulting in the formation of pores during shear. Porosity nucleated at inclusions inside the specimen. In the case of solid fraction of 50%, the shear cracking was formed through the conjugation of pores by 2d (d : average grain size) increment of Al₂O₃ push-plate motion. A cracking model based on the rearrangement of solid particles and liquid flow into the shear region consistently explained the observation result.

  The effects of Sr addition on the solidified structures and hot-tearing of Al-6mass%Mg-3mass%Si alloys cast into the I-beam shaped mold was investigated by OM, SEM-EDS observations. The area fraction of the hot-tearing region decreased from 80% to 0% with the increasing amount of Sr from 0 to 0.004mass%, due to the fining of secondary crystallized eutectics, such as Mg₂Si and α-Al phases.

  When Sr contents in Al-6mass%Mg-3mass%Si alloys were above 0.07mass%, the area fraction of the hot-tearing region increased from 0% to nearly 100%. This tendency for the hot-tearing region to increase may be caused by the crystallization of the Al-Si-Sr intermetallic compound when Sr is added by more than 0.007mass%.

  This review introduces previous literatures concerning the hot tearing susceptibility of non-ferrous alloys through two papers and reports the research trends of the world. This paper reviews the following two points : history of testing devices and hot tearing susceptibility of aluminum alloys. The next paper will review the hot tearing susceptibilities of magnesium alloys, nickel base super alloys, and copper alloys. The estimation methods of hot tearing susceptibility using the temperature dependence of solid fraction will also be introduced.

  This review, following the previous paper which reviews the history of testing devices and hot tearing susceptibility of aluminum alloys, introduces worldwide research trends on hot tearing susceptibilities of magnesium alloys, nickel base super alloys, and copper alloys. Estimation methods of hot tearing susceptibility using the temperature dependence of the solid fraction are also introduced.

  This review introduces previous literatures concerning hot tearing prediction by using thermal stress analysis. Both process parameters which were changed and hot tearing indicators which were employed are summarized. Available process parameters to predict the change of susceptibility and valuable indicators for prediction are also introduced.

  Predicting hot tearing during casting process using thermal stress analysis requires mechanical properties in the semi-solid state of alloys. This paper reviews the tensile properties in the semi-solid state of aluminum alloys from literatures reported since 2000 by following two perspectives. One is the application of mechanical properties to the constitutive equation, and the other is the effects of temperature history of test specimens on tensile properties in the semi-solid state and microstructure. We conclude that tensile test after partial solidification is more appropriate than that during partial remelting for hot tearing prediction via thermal stress analysis.