AZ31/7475方形双金属复合管气压胀形-冷缩结合工艺

Gas blow forming and contradictive cooling bonding technology of AZ31/7475 square bimetal composite tube

利用气压胀形-冷缩结合工艺成形AZ31/7475方形复合管,在450℃下,通过改变加载路径发现,成形气压不得小于3 MPa,最佳成形气压为6 MPa。实验结果表明,当保压时间一定时,终了成形气压由5 MPa增大到6 MPa,使圆角半径由6.5 mm减小到6.0 mm;而在最佳成形气压(6 MPa)下,随着保压时间由30 s延长到300 s,使圆角半径由4.0 mm减小到3.5 mm。因此,在一定条件下,增大成形气压或延长保压时间,可有效地促进圆角填充,提高成形质量。由于成形过程中复合管受到模具的约束和摩擦力的作用,使得变形主要发生在圆角处,导致方形复合管横截面上存在壁厚不均匀的现象。利用SEM观察复合管界面的结合情况,发现界面结合紧密,无裂纹、起皱等缺陷存在;通过AsB和EDS研究了界面处金属间化合物与元素的分布,并发现界面处无金属间化合物生成,无扩散过渡层存在。对界面结合强度进行了理论计算和实际测量,发现计算值和测量值相对误差约13.22%,吻合程度较好。

The AZ31/7475 square composite tubes were formed by adopting the process of gas blow forming and contradictive cooling bonding technology.At 450℃,by changing the loading path,it is found that the forming pressure should not be lower than 3 MPa,and the optimum forming pressure is 6 MPa.The experimental results show that when the holding time is fixed,with the final forming pressure increasing from 5 MPa to 6 MPa,the fillet radius decreases from 6.5 mm to 6.0 mm;while under the optimal forming pressure of 6 MPa,with the holding time increasing from 30 s to 300 s,the fillet radius decreases from 4.0 mm to 3.5 mm.Therefore,under certain conditions,increasing the forming pressure or prolonging the holding time can effectively promote the fillet filling,and improve the forming quality.Due to the constraints of the die and friction in the forming process of the composite tubes,the deformation mainly occurs at the rounded corner part,resulting in the uneven wall thickness of the square composite tube section.Scanning electron microscope was used to observe the interface bonding of the composite tubes.It is found that the interface is tightly bonded without cracks and wrinkles.The distribution of intermetallic compounds and elements at the interface was studied by angle-selective backscanning electron detector(AsB)and energy dispersive spectrometer(EDS).No intermetallic compound is formed at the interface,and there is no diffusion transition layer.The theoretical calculation and actual measurement of the interface bonding strength were carried out.It is found that the relative error between the calculated and the measured value is about 13.22%,which is in good agreement.