氏名　Rattana Borrisutthekul
学位の種類　博士（工学）
学位記番号　博甲第437号
学位授与の日付　平成19年8月31日
学位論文題目　Basic study on laser welding for dissimilar metals joint　（異種金属レーザー接合に関する基礎的研究）
論文審査委員
　主査　教授　武藤　睦治
　副査　教授　福澤　康
　副査　教授　岡崎　正和
　副査　准教授　井原　和久
　副査　長岡工業高等専門学校機械工学科　准教授　宮下　幸雄

• 論文目次
• 論文要旨
• 論文審査の結果の要旨

［平成19（2007）年度博士論文題名一覧］ ［博士論文題名一覧］に戻る．

Abstract　p.ii
Table of Contents　p.iii
List of Figures　p.vi
List of Tables　p.xi
List of Publications　p.xii
Acknowledgment　p.xiv
Chapter 1.　Introduction　p.1
　1.1　General backgrounds　p.2
　1.2　Welding technology　p.4
　1.3　Dissimilar metals welding conceptd　p.13
　1.4　Investigation of joining technique of Fe/Al　p.16
　1.5　Investigation of joining technique of Mg/Al　p.17
　1.6　Conclusions　p.19
　1.7　Scope of the present worl　p.20
Chapter 2.　Experimental Procedure and FEM Model Definitions　p.30
　2.1　Materials　p.31
　2.2　Experimental and procedure and equipments　p.33
　2.3　FEM model definitions　p.45
Chapter 3.　Dissimilar Laser Welding between Steel and Aluminum　p.53
　3.1　Introduction　p.54
　3.2　A concept for suppressing intermetallic compound layer formation　p.55
　3.3　Eperimental procedures　p.56
　3.4　FEM simulation　p.59
　3.5　Results and discussion　p.61
　3.6　Conclusions　p.72
Chapter 4.　Dissimilar Laser Welding between Magnesium Alloy and Alluminum Alloy　p.75
　4.1　Introduction　p.76
　4.2　Experimental procedures　p.78
　4.3　Results and discussion　p.79
　4.4　Conclusions　p.88
Chapter 5.　Application of Al-12Si Filler Wire to Laser Welding between Magnesium Alloy and Aluminum Alloy　p.92
　5.1　Introduction　p.93
　5.2　Butt-welding　p.94
　5.3　Edge-lap welding　p.105
　5.4　Conclusions　p.119
Chapter 6.　Overall Conclussions and Future Prospects　p.122
　6.1　Overall conclusions　p.123
　6.2　Future Prospects　p.128

　Since automotive industries need to reduce weight of vehicles for improving its fuel consumption efficiency, the lightweight metals such as aluminum alloy, magnesium alloy and so on, have been introduced as raw materials for production of vehicle components. When those components are necessary to be assembled, dissimilar metals welding technology is the first requirement. It has been known that almost dissimilar metals welding between different structural metals and alloys form the intermetallic compound phase during welding. In the present study, based on new dissimilar metals welding concepts proposed, new laser dissimilar metals welding techniques for joining combinations have been developed.
Chapter 1 Introductions: General backgrounds of welding, concepts for dissimilar metals welding technology, and currently developed welding methods for joining Fe/Al and Al/Mg were reviewed. Then, scopes and objectives of the present study were indicated.
Chapter 2 Experimental Procedures and FEM Model Definitions: The chemical compositions, mechanical properties, and physical properties of steel, magnesium alloy and aluminum alloys used were summarized. Details of experimental procedures were indicated. Moreover, the methods for estimating the heat transfer coefficient and laser absorption rate were explained, which were used for FEM analysis of transient temperature distribution during laser welding.
Chapter 3 Dissimilar Laser Welding between Steel and Aluminum Alloy: In welding of high strength steel and A6022 aluminum alloy, the concept of suppression of intermetallic compound formation was introduced. The welding technique that we proposed for suppression of intermetallic compound formation was to control heat flow around the welding zone by using backing block. Effect of backing block metal on formation of intermetallic compound was discussed. The joining strength was strongly dependent on the thickness of intermetallic compound layer. It could be concluded that backing block was significantly effective for controlling heat flow and consequently thickness ofintermetallic reaction layer.
Chapter 4 Dissimilar Laser Welding between Magnesium Alloy and Aluminum Alloy: Based on the suppression of intermetallic compound phase concept, laser welding of AZ31 magnesium alloy/A5052 aluminum alloy by controlling penetration depth in lap joint was investigated.　In experiment, two types of welding configurations were applied. Using center-line welding of lap joint, it was found that the intermetallic compound layer formed at interface between two metals significantly degraded the joining strength. The edge-line welding of lap joint was also carried out, which could easily control the thickness of intermetallic compound layer and successfully obtained higher load resistance of joint. Maximum failure load obtained was about 1040 N, which was about 74 percents of yield load of A5052.
Chapter 5 Application of Al-12Si Filler Wire to Laser Welding between Magnesium Alloy and Aluminum Alloy: According to concept of intermetallic compound phase modification, Al-Mg intermetallic compound was attempted to transfer to Mg2Si during laser welding of AZ31/A5052 by applying Al-12Si filler wire. Butt-welding with and without using Al-12Si filler wire was studied. Also edge-lap joint welding using single laser beam and dual laser beam was investigated.
-For butt-welding, in case of joint without filler wire, the highest joining strength obtained was 80 MPa and the joining strength depended on Al-Mg intermetallic compound morphology, which was changed with variation of welding speed. In case of joint with filler wire, thin layer of Mg2Si and eutectic phase along the fusion line could be formed and resulted in the improved joining strength compared to the direct joint without filler wire. The highest joining strength obtained was about 119 MPa, which was about 119 percents of yield strength of A5052.
-For edge-lap welding, the results for single beam laser welding showed inability to obtain shallow penetration depth of molten zone, which contributed to low failure load obtained. The maximum failure load was about 880 N. Application of dual beam laser welding could well control the penetration depth. Increase in welding speed resulted in decrease in welding width and penetration depth. Moreover, increase in feed rate could increase the welding width and penetration depth. It was found that failure load was increased with increasing the welding width. The maximum failure load obtained was 1734 N, which was about 123 percents of yield load of A5052.
Chapter 6 Overall Conclusions and Future Prospects: Overall conclusions and future prospects have been given.

　本論文は、「Basic study on laser welding for dissimilar metals joint（異種金属レーザー接合に関する基礎的研究）」と題し、6章より構成されている。
　第1章「緒論」では、異材接合技術と概念、およびFe/AlおよびAl/Mg接合に関する従来の研究の概要を示すとともに、本研究の目的と範囲を述べている。
　第2章「実験方法とFEMモデル」では、供試材であるアルミニウム合金、マグネシウム合金および鋼について、接合に関連する材料特性について述べるとともに、接合試験の詳細について述べている。また、FEM解析に必要な諸物性を求める試験についても示すとともに、FEM解析の詳細についても述べている。
　第3章「鋼とアルミニウム合金の異材レーザー接合」では、接合強度を低下させる金属間化合物反応層をできるだけ抑えるため、熱伝導率の異なる接触ブロックを用いることにより、接合部の温度履歴を制御する手法を提案している。本手法により、熱伝導率の大きな接触ブロックほど金属間化合物層厚さは薄くなり、接合強度も高くなることなどを明らかにしている。
　第4章「マグネシウム合金とアルミニウム合金の異材レーザー接合」では、金属間化合物層の生成を抑える手法として、溶け込み深さを制御する手法について検討し、重ね継手の中央部接合では金属間化合物反応層が生成されるが、重ね継手の隅肉溶接では、容易に金属間化合物層の生成を抑制できること、また、その場合の接合強度はアルミニウム合金の降伏強度の約74％にまで改善されることなど、を明らかにしている。
　第5章「Al-12Siフィラーワイヤーを用いたマグネシウム合金とアルミニウム合金のレーザー接合」では、金属間化合物の組成を変えることによる効果で良好な接合体を得るという考え方に基づき、Al-12Siフィラーワイヤーを用い、Al-Mg反応相を高融点のMg2Si相に変化させることを試みている。この手法を突合せ溶接と重ね隅肉溶接に適用し、突合せ溶接では、接合界面に薄いMg2Si反応層が形成され、接合強度も降伏強度の約1.2倍と優れた接合強度が得られること、重ね隅肉溶接では、単一レーザービームでは溶け込みが深く良好な接合体を得ることは難しいが、デュアルレーザービームを用いることにより、溶け込みが浅く、金属間化合物層の形態も良好な接合体が得られ、接合強度も降伏強度の約1.23倍ときわめて高いこと、などを示している。
　第6章「結論」では、本論文で得られた結果を要約するとともに、本論文に基づき、今後の展開についても論じている。
　よって、本論文は工学上及び工業上貢献するところが大きく、博士（工学）の学位論文として十分な価値を有するものと認める。