Research On Technological Basis For Gas Blow Forming-cooling Contraction Bonding Of AZ31/7475 Bimetal Composite Tubular Part

Gas blow forming-cold contraction bonding process was carried out for AZ31/7475 bimetal tubular part in this subject. The composite tube is formed by gas blow forming during heating and the holding force is provided by cooling contraction combination during cooling, which achieves the connection of AZ31 magnesium alloy and 7475 aluminum alloy.The basic data in circumference direction of AZ31 magnesium alloy and 7475 aluminum alloy such as flow stress, elongation and strain rate sensitivity exponent were obtained by the unidirectional hot tensile tests at different strain rates and temperatures, which provided a basis of finite element analysis and forming parameters. The results showed that the temperature parameters ranging from 420 to460℃ are qualified for synchronous gas blow forming and the plasticity of AZ31 and 7475. The velocity jump tests were carried out at 440℃ to measure the value of m and K.A FEA software MSC.Marc was used to simulate the forming process about free bulging and filling bulging and to analyze the deformation rules of AZ31/7475 bimetal tubular part on the basis of the value of material constant above. The loading pressure, the clearances between the Mg/Al bimetal tubular part and the friction coefficients between the outer Mg tube and mold have effect on the wall thickness distribution.Experiments for gas blow forming-cooling contraction of bimetal tube were carried out at intervals of 10℃ ranging from 420℃ to 470℃. The results showed that the largest extreme expansion ratio increases from 32.3% to 39.3% with temperature increasing, only by about 7%. The suitable forming temperature and gas pressure profile were summarized. The numerical and experimental date for thickness distribution matched well, which error rate was less than 10%.The experiments on AZ3/7475 bimetallic composite tube with outer diameter of 33 mm formed by gas blow forming-cold contraction bonding process was performed at 420 ℃. The wall thickness distribution of as-formed bimetallic composite tube is uniform in axial direction and circumferential direction.The interface of bimetal tube bonds well. The holding force of composite tube wascalculated theoretically by using Lame Formula considering bimetallic composite tube as two combined cylinders with interference fit. The results showed the contact pressure between internal and external tube is about 2.96 MPa.Gas blow forming-cold contraction bonding process can be also used to the forming of composite tube such as stainless steel/titanium and super alloys/ titanium.It provides a new method for preparation of bimetallic composite tube.