溶接欠陥防止技術の開発

Abstract

A development mechanism of the weld defects (blowhole, porosity) generated by inclusion of bubbles has been investigated using an original technique to utilize a specific phenomenon in microgravity environment. Since the bubbles generated in a melt pool are to rise to the surface by receiving a buoyant force under ground gravitational environment, all of the bubbles are not always retained in welded metal, makes it extremely difficult to analyze the cause of bubble generation. However, it becomes easy to analyze the cause of the bubble generation under microgravity environment, because the bubbles can be frozen into welded metal as a result of the obsence of buoyant force in the microgravity environment. Development mechanism of the weld defects has been examined using this technique for the electron beam welded section of A2219 aluminum alloy. It was identified that hydrogen included in welded base metal was the cause of the defects. A defect prevention method (reduction of base metal hydrogen and hydrogen fixation) was proposed.

微小重力環境特有の現象を活用する独創的な手法により、気泡が原因となり発生する溶接欠陥(ブローホール、ポロシティ)の発生機構を調査した。重力環境下(地上)では溶融池内に発生した気泡は浮力を受け表面に浮上するため、気泡のすべてが溶接金属中に残存せず気泡発生原因の解析を極めて困難としている。しかし微小重力環境下では浮力が発生しないため気泡を溶接金属中に凍結でき、気泡発生原因の解析が容易となる。この手法を用いてA2219アルミニウム合金電子ビーム溶接部の欠陥発生機構を調査し、溶接母材中に含まれる水素が欠陥の原因であることを特定するとともに、欠陥防止法(母材水素低減と水素固定化)を提案した。