工藝:氣孔的產生和避免(中英)

為什么會出現氣孔

1.1激光焊接的小孔內部處于一種不穩定振動狀態,小孔和熔池的流動非常劇烈,小孔內部的金屬蒸汽向外噴發引起小孔開口處的蒸汽渦流,將保護氣體(Ar)卷入小孔底部,隨著小孔向前移動,這些保護氣體將以氣泡形式進入熔池。因Ar溶解度極低,再加上激光焊接的冷卻速度很快,氣泡來不及逸出而被殘留在焊縫,形成氣孔。另外由于保護不良而引起的。在焊接過程中,氮從外部侵入熔池,氮在液態鐵中的溶解度與氮在固態鐵的溶解度有很大的差異,因而在金屬的冷卻凝固過程中。 由于氮的溶解度隨溫度的下降而降低,當熔池金屬冷卻到開始結晶時,溶解度將發生大幅度的突然下降,此時氣體大量析出形成氣泡,如果氣泡的上浮速度小于金屬結晶速度,則生成氣孔。


激光熔焊抑制氣孔方式

1、通過焊前表面處理方式抑制焊接氣孔

焊前表面處理是控制鋁合金激光焊縫冶金氣孔的有效方法,通常表面處理方法有物理機械清理、化學清理。

Why do pores appear


1.1 The inside of the laser welded hole is in a state of unstable vibration, and the flow between the hole and the molten pool is very intense. The metal steam inside the hole explodes outwards, causing steam vortex at the opening of the hole, which will inject the protective gas (Ar) into the bottom of the hole. As the hole moves forward, the protective gas will enter the molten pool in the form of bubbles. Because the solubility of Ar is very low, coupled with the cooling speed of laser welding is very fast, the bubbles can not escape and are left in the weld, forming pores. In addition due to poor protection caused by. During the welding process, nitrogen intrudes into the molten pool from the outside, and the solubility of nitrogen in liquid iron is very different from that of nitrogen in solid iron, thus during the cooling and solidification process of the metal. Since the solubility of nitrogen decreases with the decrease of temperature, when the molten pool metal is cooled to the beginning of crystallization, the solubility will suddenly drop sharply, and a large number of gases will precipitate to form bubbles. If the floating speed of the bubbles is less than the crystallization speed of the metal, pores will be formed.

Porosity suppression by laser welding

1 Inhibit welding pores by surface treatment before welding

The surface treatment before welding is an effective method to control the metal pores in laser welding of aluminum alloy. The surface treatment methods usually include physical mechanical cleaning and chemical cleaning.




經過對比,采用化學方法處理試板表面(金屬清洗劑清洗-水洗-堿洗-水洗-酸洗-水洗-干燥)的流程處理最好。其中堿洗用25%NaOH(氫氧化鈉)水溶液去除材料表面厚度,酸洗用 20% HNO3(硝酸)+2% HF(氟化氫)水溶液中和殘留的堿液。試板表面處理后在24小時內實施焊接,試板處理后停留時間較長時焊前裝配再用無水酒精擦拭。


2、通過焊接工藝參數抑制焊接氣孔

焊縫氣孔的形成除了與焊件表面處理質量有關,還與焊接工藝參數相關。焊接參數對焊縫氣孔的影響主要體現在焊縫熔透情況,即焊縫背寬比對氣孔的影響。





通過測試可知,焊縫背寬比R>0.6時可以有效改善焊縫中鏈狀氣孔的集中分布,當背寬比R>0.8 時,可以有效改善焊縫中大氣孔的存在,并很大程度上消除了焊縫中氣孔的殘留。


3、通過正確選擇保護氣體及流量抑制焊接氣孔

保護氣體的選用直接影響到焊接的質量、效率及成本,激光焊接過程中,正確的吹入保護氣體可以有效減少焊縫氣孔。

After comparison, the process of chemical treatment of the test plate surface (metal cleaning agent cleaning - water washing - alkali washing - water washing - pickling - water washing - drying) is the best. Among them, 25%NaOH (sodium hydroxide) aqueous solution is used to remove the surface thickness of the material in alkaline washing, and 20% HNO3 (nitric acid) +2% HF (hydrogen fluoride) aqueous solution is used to neutralize the residual lye in pickling. After the surface treatment of the test plate, welding shall be carried out within 24 hours. If the test plate stays for a long time after treatment, the assembly shall be wiped with anhydrous alcohol before welding.

2. Inhibit welding porosity through welding process parameters

The formation of weld porosity is not only related to the quality of weldment surface treatment, but also related to welding process parameters. The influence of welding parameters on the porosity of the weld is mainly reflected in the weld penetration, that is, the influence of the weld back width ratio on the porosity.




如上圖,采用Ar(氬氣)和He(氦氣)對焊縫表面進行保護,在鋁合金激光焊接過程中,Ar和He對激光的電離程度不同,造成焊縫成形不盡相同。結果可見,選用Ar作為保護氣體所得焊縫的氣孔率整體少于選用He作為保護氣體時焊縫的氣孔率。



同時我們也要注意,氣流量過?。?lt;10L/min)焊接產生的大量等離子體無法吹走,使得焊接熔池不穩定,氣孔形成幾率增加。氣體流量適中(15L/min左右)等離子體得到有效控制,保護氣對溶池起到了很好的防氧化作用,氣孔最少。過大的氣流量伴隨過大的氣體壓力,使得部分保護氣混入溶池內部,使氣孔率上升。


受材料本身性能影響,在焊接過程中不能完全避免焊接無氣孔現象,只能降低氣孔率。

As shown in the figure above, Ar (argon) and He (helium) are used to protect the weld surface. In the process of laser welding of aluminum alloy, the degree of ionization of Ar and He to the laser is different, resulting in different weld forms. The result shows that the porosity of the weld obtained by using Ar as the shielding gas is lower than that by using He as the shielding gas.

At the same time, we should also note that a large amount of plasma generated by welding with too small gas flow (<10L/min) cannot be blown away, making the welding pool unstable and increasing the probability of porosity formation. The gas flow is moderate (about 15L/min), the plasma is effectively controlled, and the protective gas plays a good anti-oxidation effect on the solution pool, with the least porosity. Excessive gas flow accompanied by excessive gas pressure causes part of the protective gas to mix into the solution pool, resulting in increased porosity.

Affected by the properties of the material itself, the phenomenon of non-porosity can not be completely avoided in the welding process, and the porosity can only be reduced.