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 blister's appearance, at first they appears at low temperature and secondly at the temperature more than about 425°C.