Properties Of FSW Lap Joint Of Aluminum And Optimization Of Tools

Lap joint is widely applied in the field of transportation and can be welded by friction stir welding(FSW).In this thesis,eight rotational tools are designed and fabricated in order to optimize the tool geometry and then improve the property of lap joint.These tools can be divided into two types: tools with various thread geometry and tools with various pin length.Choosing 2024-T4 aluminum alloy as research subject,effect of tool geometries on cross section and tensile-shear property of FSW lap joint were discussed in detail.Based on tools with various thread geometry,the experiment of FSW lap joint were performed.The results show that full-threaded pin(F-pin)makes material accumulated zone(MAZ)locate near pin tip.Tip-threaded pin(T-pin)not only accumulates material near pin tip,but exerts downward load on the material near the starting position of thread.Bottom-threaded pin(B-pin)owns two MAZs.One is located at ending position of thread,the other is near pin tip.MAZ attained by reverse-threaded pin(R-pin)is located in the center of stir zone(SZ).The experimental results of tensile-shear test show that when the advancing side bears the load(configurations A),FSW lap joint by T-pin owns the higher shear failure load compared to the other three pins.When the retreating side bears the load(configurations B),the shear failure load of joint by T-pin is higher than those by B-pin and R-pin.Based on tools with various pin length,the experiment of FSW lap joint were performed.The results show that when the pin with 3mm length is used,the hook at AS presents the horizontal distribution and the cold lap at RS extending into SZ is relatively longer.When the pin length increases to 4mm,hook and cold lap defects obviously bend upward.When the pin length reaches 5mm,the heights of hook and cold lap defects decrease while the cold lap extending into SZ shrinks.The results of tensile-shear test show that when the pin length increases from 3mm to 5mm,the shear failure load firstly decreases and then increases.Under the 3mm-length pin,FSW lap joints owns the maximum shear failure load,and the values under configurations A and B are 20825 N and 25665 N,respectively.In order to avoid hook defect,the 2mm pin length is used.The effective bonding is successfully obtained when the pin does not penetrate into lower sheet.The lap shear failure load by 2mm-length pin is 12185 N.