This study focuses on the microstructure and mechanical properties of the joints of Q235 mild steel, which was formed by the friction stir welding (FSW). The results indicated that, after the FSW, the heat-affected zone (HAZ) of the retreating side (HAZ_RS) and the HAZ of the advancing side (HAZ_AS) recovered under the influence of the heating cycle. The transformation of the phases in the thermo-mechanically affected zone (TMAZ) of the retreating side (TMAZ_RS), the stir zone (SZ) and the TMAZ of the advancing side (TMAZ_AS) generated the pearlite and acicular ferrite. The continuous dynamic recrystallization occurred in all the three zones, whereas the grains were refined. The SZ mainly consisted of D₁, D₂ and F shear textures, while the TMAZ_AS was made up of only the F shear texture. The fine-grained structure, pearlite and the acicular ferrite improved the hardness and tensile strength of the joint. Its ultimate tensile strength was 479 MPa, which was 1.3% higher than that of the base metal. However, the uniform elongation was 16%, which showed a decrease of 33%. The fracture was a ductile fracture with the appearance of dimples. Besides, the joints of the FSW showed an excellent bending performance.

这项研究的重点是Q235低碳钢接头的微观组织和力学性能，该接头是通过搅拌摩擦焊（FSW）形成的。结果表明，在FSW之后，后退侧的热影响区（HAZ _RS）和前进侧的热影响区（HAZ _AS）在加热循环的影响下恢复。退避侧的热机械影响区（TMAZ _RS），推进侧的搅拌区（SZ）和TMAZ（TMAZ _AS）中的相变产生珠光体和针状铁素体。在这三个区域中都发生了连续的动态再结晶，而晶粒被细化了。SZ主要由D _1组成，D ₂和F剪切纹理，而TMAZ _AS仅由F剪切纹理组成。细粒结构，珠光体和针状铁素体提高了接头的硬度和拉伸强度。其极限抗拉强度为479 MPa，比母材高1.3％。但是，均匀伸长率为16％，降低了33％。骨折是具有酒窝外观的延性骨折。此外，FSW的接头表现出出色的弯曲性能。