The corrosion behavior of clad sheets of aluminum alloys in the automotive radiator coolants was studied for 99.7%Al, Al-1.0%Zn and Al-2.0%Zn alloys clad on the A3003 core alloy. The materials were subjected to elevating-temperature immersion tests and electrochemical measurements with the coolant pH varying in the 7.5-10.0 range. Significant pitting corrosion with a black colored oxide film formation occurred on these clad sheets in the coolants at pH of 9.5 and 10.0. For every clad sheet, the depth of pitting corrosion exceeded the thickness of the sacrificial anode clad alloy and progressed to half of the tube thickness in 60 days. In the anodic polarization of A3003, the steady-state current density was high and the pitting potential reached to more than 2000 mV vs SCE at pH 10.0, even though the open-circuit potential was between －1600 and －500 mV vs SCE. The polarization behavior of Al-1.0Zn was similar to that of A3003. These results indicate the ineffectiveness of cathodic protection by cladding Al-1.0Zn as the sacrificial anode. Based on the experimental results, a corrosion mechanism for the clad sheet in a weakly alkaline solution has been proposed related to the oxide film formation and localized corrosion without the cathodic protection effect.
By conducting In-situ XRD measurement during tensile deformation while oscillating the tensile tester, it was possible to measure the change in dislocation density of a pure aluminum alloy having coarse grains with the grain size of 20 μm. In the coarse-grained material, the dislocation density during tensile deformation changed through four regions, as in the case of the fine-grained material. Since the dislocation multiplication start stress was very low at 22MPa, the elastic deformation region was very short. Thereafter, the dislocations multiplied rapidly, but when the stress and dislocation density reached 33 MPa and 1.57×1014m-2, respectively, the dislocation multiplication rate was greatly reduced. This is considered to be due to the low dislocation density required to progress the deformation by plastic deformation in coarse-grained aluminum.
The possibility of the incremental flattening of the bends of 5052 aluminum alloy sheets was experimentally examined by computerized numerical control (CNC) incremental hammering. The experimental results indicated that flattening was possible and that the metal flow behavior depended on the rotational direction of the tool and the hammering pitch. It was also clarified that the transcription accuracy of the envelope surface of the tool was improved by four-pass incremental flattening and that the thickness of the flattened part was greater than that of the mother sheet.