In recent times, the use of aluminum alloys in large-scale structures has been widely advocated. In view of the maintenance and administration of these structures, the implementation of a simple repair methodology holds immense significance. It is imperative to clearly elucidate this methodology and its fatigue-life extension effect. In our study, we examined the effect of a simple repair technique using resin on the fatigue life of aluminum alloys featuring simulated cracks. Our findings confirm the following four points: Firstly, the fatigue life of repaired specimens increased by up to 1.8 times. Secondly, the initiation and growth life of cracks were extended in the repaired specimens. Thirdly, the crack growth rate in the specimens was slower, and fourthly, the striation width was smaller in the specimens. These results strongly suggest that the wedge effect of the resin has suppressed fatigue crack initiation and propagation.

The bendability of extruded Al-4.4Zn-1.4Mg (mass%) alloy flat bars with 1.4 mm thickness having two types of microstructures which are fibrous and recrystallized is evaluated by a Verband der Automobilindustrie (VDA) bending test without pre-strain. The recrystallized specimen has better bendability than the fibrous one. The texture condition nearby the surfaces affects the VDA bendability the most. However, the microvoid formations also contribute in faster cracking phenomena during the load drop of the VDA bending test.

A model experiment for in-line hot rolling was proposed, and its effectiveness in reducing surface cracking and improving the mechanical properties of cast strips of AC7A Al-Mg alloy was investigated. The strips were cast using an unequal-diameter twin-roll caster at 60 m/min. The strips had a width of 100 mm, and were immediately cut to a length of 200 mm and hot rolled at temperatures of 300, 350, 400, 450 and 500°C. The temperature of the strip surface was measured using a K-type thermocouple. The center area in the width direction of the strips was hot rolled. The thickness of the as-cast strips was 2 mm, and the width of the rolled region was 20 mm. The roll diameter was 70 mm, and the rolling speed was 15 m/min. The thickness reduction caused by hot rolling ranged from 19 to 42%. Surface cracking was reduced by the in-line hot rolling process. The hot-rolled strips were cold rolled down to a thickness of 0.5 mm and then annealed, and tensile tests were conducted. The in-line hot rolling process induced shear deformation of the microstructure. The most appropriate conditions for in-line hot rolling of AC7A were a thickness reduction of 27% and a temperature of 350°C, judging from the tensile strength and elongation results.

In this study, the effects of the roll load and superheating on the appearance of surface defects in Al-Mg and Al-Si alloy strips cast using a high-speed twin-roll caster were investigated. The band zone that existed in the center of the thickness direction was investigated. The alloy compositions were Al-4.8%Mg and Al-Si with Si contents of 1, 2, 3 and 11%. The diameter and width of the copper roll in the twin-roll caster were 300 and 50 mm, respectively. The superheating temperature of the molten metal was 5 and 50°C, and the roll load was varied from 2 to 88 N/mm. A roll speed of 30 m/min was utilized. The existence of surface cracks was investigated by penetrant inspection and bending test. The amount of surface cracking in the Al-Mg alloy was affected by the roll load, and the number of surface cracks decreased with decreasing roll load. Surface cracks occurred more easily in the Al-4.8%Mg alloy than in the Al-Si alloys. The degree of cracking could not be reduced by cold-rolling. In the Al-Si alloys, the ripple marks were affected by the Si content and the roll load. In the Al-3%Si alloy, ripple marks were produced, and worsened as the roll load increased. A specimen for observation of the microstructure near the roll bite was obtained by performing a roll-stop during casting, and observed using Weck’ s reagent. A band zone was found to exist. The band zone in Al-Si consisted of globular crystals, and that in Al-Mg consisted of equiaxed dendrites and Mg-richareas.