SiCp/6092Al復合材料攪拌摩擦焊接頭的疲勞行為研究

SiCp/6092Al復合材料攪拌摩擦焊接頭的疲勞行為研究Fatigue behavior of friction stir welded SiCp/6092 Al composite

為獲得高質量、疲勞性能優異的SiCp/6092Al復合材料攪拌摩擦焊接頭，對3 mm厚的T6態SiCp/6092Al復合材料軋制板材分別在50 mm/min的低焊速和800 mm/min的高焊速下進行攪拌摩擦焊接，轉速恒為1000 rpm。研究了焊速對接頭的組織演變及拉伸性能、高周疲勞性能的影響。試驗結果表明，高焊速接頭表面“魚鱗紋”較明顯，且橫截面方向的焊核區形貌與低焊速接頭具有一定差異。焊速增加顯著提高了FSW接頭的硬度和拉伸強度，而對于表面未打磨的接頭卻未能提高接頭的疲勞極限，高焊速接頭表現出較低的高周疲勞極限。不同循環應力加載下，試樣表現出不同的斷裂方式。高應力下，低焊速接頭由表面“魚鱗紋”凹痕引起疲勞斷裂，而高焊速接頭是由焊核區底部的渦旋區流動不充分引起斷裂。在低應力下，未打磨試樣均由接頭表面“魚鱗紋”凹痕引起疲勞斷裂，三維表面形貌顯示高焊速接頭表面粗糙度較大是造成疲勞極限較低的原因。經過打磨拋光后的光滑表面接頭與表面未打磨接頭相比疲勞極限得到顯著提高，且高焊速下的光滑表面接頭表現出更高的疲勞極限，光滑表面接頭在疲勞測試時均斷在了最低硬度區及其附近的區域。

To acquire high quality and excellent fatigue property of friction stir welded SiCp/6092Al composite joint, 3 mm-thick rolled SiCp/6092Al composite plates with T6 state were conducted by friction stir welding (FSW) at a constant rotational rate of 1000 rpm, and at a low welding speed of 50 mm/min and a high welding speed of 800 mm/min, respectively. Microstructure evolution, mechanical properties and high cycle fatigue behavior of the FSW joints were evaluated. The results showed that high welding speed resulted in a more rough surface of scale-like ripple and the morphology of the nugget zone was different from that of the joint at low welding speed. Significant enhancement of the hardness and tensile strength were achieved in the joints at the high welding speed, but the fatigue properties were not improved for the joints with unpolished surfaces. For the joints with polished surfaces, obviously enhanced fatigue limit was achieved at the high welding speed of 800 mm/min compared to that of the joint at the low welding speed of 50 mm/min. Different fracture characteristics were observed in the specimens with unpolished surfaces at various cyclic stress loading. Under a low cyclic stress loading, crack initiated at the scale-like ripple on the surface of the specimen. Under a high cyclic stress loading, crack also initiated at the scale-like ripple at the low welding speed, while the crack initiated at the swirl zone in the bottom of the nugget zone at the high welding speed of 800 mm/min. The results of the three-dimension surface topography showed that a large surface roughness was achieved on the surface of the joint at the high welding speed, resulting in lower fatigue limit compared to that of the joint at the low welding speed. For the specimens with polished surfaces, higher fatigue limit was obtained than that of the specimens with unpolished surfaces. In this case, the joint at the high welding speed exhibited higher fatigue limit than that of the joint at the low welding speed, and all the specimens failed at the lowest hardness zone and nearby.

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