Osamu Yoshimura

Study on wave forms of electric current in anodic oxidation of aluminium by oxalic acid process

Using half wave rectification obtained from selemium rectifier, anodic oxidation of aluminium by oxalic acid process is investigated as follows:1) Anodic corrosion and its protection of negative current.2) Observation of wave forms of electric current by oscillograph.3) Properties of oxide film anodized under various conditions of temperature and concentration of electrolyte.Results are summarized as follows:(1) In 0.5 and 3.5% concentration of electrolyte, anodic corrosion occurs when only half wave rectification is used. The lower the concentration of electrolyte, the higher the negative current necessary to protect its corrosion. It is about 0.1-0.2A/dm2 (root mean square value) for 1A/dm2 positive current (mean value). With an increase of negative current and a decrease of concentration of electrolyte, specific corrosion resistance becomes better. But specific abrasion resistance slightly falls with an increase of negative current.(2) While the anodic oxidation is normally proceeding, distortion of wave form in oscillograph is observed, but this distortion disappears when anodic corrosion begins to occur.(3) As a general tendency of the effect of temperature and concentration of electrolyte on the properties of oxide film anodized under constant positive and negative current, specific corrosion resistance becomes better with lower concentration and higher temperature, but specific abrasion resistance becomes better with lower temperature.

STUDY ON BLISTER OF ALUMINIUM SHEETS (PART 4)

The authors studied the influence of heating temperature on 99.97%Al, 99.8%Al 99.5%Al, 99.0% Al (main impurities Fe and Si) and 1%Mg-Al Alloy sheets of the same gas content. In this report, gas grade 3 and 7 according to the measuring method shown in this paper part 2 were studied. The relation between heating temperature and the blister of the sheets which was hot rolled with or without slab soaking were also described.

STUDY ON BLISTER OF AL-SHEETS

It is said that the blister of Al-sheets are caused by gass involved in slabs which expands when annealed and appears as blisters, and it has been beleived that this gas is contained in molton aluminium at melting, which consists almost of H2-gass. It is however, cleared by investigating the shapes, the sizes and the time of their appearance that they are caused not so simply and their constituents is rather complicated. Cutting out the blister and examining it by electron difraction. I recognized the rays of graphite, Al2O3, Al, respectively according the kinds of blisters, and that graphite, oil, air, and H2-gass can also be considered as the causes of blisters.Further, I tried statistic control analysis based on the data of practical operation in order to investigate the factors of causes of blisters, and noted that pre-heating of slabs before hot-rolling has great influence on blisters. It is also studied that, when annealing sheets, if the temperature is below about 420°C it has no influence on number of blisters or size of blisters, indefferently to the time and degree of temperature of annealing. And when it is above 425°C. blisters increase by great degree.By analysing blisters it is noted that blister contains more volume of Si than the other parts do.There are two steps in a process of blisters appearance, at first they appears at low temperature and secondly at the temperature more than about 425°C.

THE EFFECT OF MELTING CONDITIONS ON MECHANICAL PROPERTIES OF ANNEALED ALUMINUM SHEETS (PART 1)

As regards the mechanical properties of annealed aluminum sheets, the percentage of virgin ingots in charge is seemed to give extremely an important effect. The more it decreases, the mechanical properties decrease and in higher percentage of return scrap in charge its tendency becomes severe.By the results of study that was made on from 99.6 to 99.8 percent purity of aluminum, the more percentage of return scrap increases, the more the tensile strength and elongation decrease together and in the percentage of return scrap until 30 percent those decrement is rapid and then after it becomes slow.There results are seemed to show that aluminum oxide in its melt is most effective at all. As its proof, a recovery of mechanical properties has recognized. In melting process of the melt of return scrap only, holding-treatment at 800°C have recovered its mechanical properties to the nearly same value of charge of 10 percent of return scrap.