Study On The Resistivity Of 7050 Aluminum Alloy And Susceptibility Of Al, Cu And Ti

In this paper the changes of resistivity of 7050 alloy in solid and from solid to liquid under different heating conditions were measured, a comprasition of the resistivity and its microstructures in different temperatures in the ingots cast by DC (Direct Chilling Casting) and LFEC (Low Frenquency Electromagnetic Casting), and the change rules of the resistivity of 7050 alloy were obtained. At the same time, an apparatus with high temperature for susceptibility measurement was built by ourself, by which the susceptibilities and their changes of pure Al,Cu and Ti from room to high temperature in different heating conditions were measured, and it is the first time to measure the effects of strain on susceptibilities of Al,Cu and Ti. A series data were obtained, which is useful to discribe the microstructure of the materials.The resistivity of DC and LFEC 7050 aluminum alloy was measured. The results show that the p-T curve is linear approximately from room temperature to 500℃, there is a slope turning point about at 250℃. The increase in crystal lattice scatter in high temperature is the main reason of the resistivity rise below 250℃. While over 250℃, more solute atoms come intoα-Al matrix, so that solute scatter enhances obviously, which results in an increases in resistivity and a turning point on the p-T curve. The room temperature resistivity of the specimens is reduced and the slope turning point of p-T curve moves towards the high temperature after the casting samples were measured from room temperature to 500℃or were annealed at 360℃, which shows that casting inner stress of the alloy was removed, defects decrease and alloying elements became uniform. The room temperature resistivity of LFEC 7050 alloy samples is higher than that of DC, but the ascending amplitude of the p-T curve of LFEC samples is larger than that of DC with temperature rise, and that both the solidus and liquidus are higher than those of DC, which shows the intracrystalline solute cotent of LFEC spacimens is high. When the temperature is over 830℃, the resistivity of liquid 7050 alloy rapidly increases. At the solidus temperature the p-T curve has an abrupt increase. Moreover the resistivity is still increased when the temperature falls from 900℃to 600℃, which mybe resulted from the solute clusters dissolving and more solutes dissloved into liquid a-Al. The resistivity of DC samples is higher than that of LFEC from 900℃to room temperature.An apparatus for susceptibility measurement was developed by ourself, by which the susceptibilities of pure metals, such as Al, Cu, Ti, Ag and Zn were measured. The measured values are nearly equal to standard ones. The maximum deviation is less than 4.02%. Theχg-T curves of pure Al and pure Ti from room temperature to 750℃are nearly the same as those pubilished in documents, which shows that the apparatus has enough accuary at room temperature and heating to 750在. The susceptibilities of weakly magnetic metal Al,Cu and Ti increase after deformation, and decrease after annealling. The susceptibility of pure Al rapidly falls during heating 0.5 hour at 600℃, and falling reduces with increase in the heating time; falling is small when the temperature below 300℃. The susceptibility of Al increases with increase in strain. The susceptibilities of Cu and Ti increase a little when the strain is less than 20%. However, their susceptibilities increase rapidly when the strian is larger than 20%.