With the growth in importance of the aluminium industry, has come increased demand to invest into the quality improvement of the different aluminium based hot extruded products. One of the main mechanisms, which can influence deformation at high temperature within the 6xxx aluminium, is linked to the presence of the AlFeSi intermetallic phases. These phases severely restrict hot workability when present as hard and brittle plate-like precipitates b-AlFeSi. Damage initiation occurs in these alloys by decohesion or fracture of these intermetallic inclusions. The understanding and modeling of the deformation and fracture behavior of aluminium alloys at room and at hot working temperature is very important for optimizing manufacturing processes such as extrusion. The ductility of 6xxx aluminium alloys can be directly related to chemical composition and to the microstructural evolution occurring during the heat treatment procedures preceding extrusion if proper physics based deformation and fracture models are used. In this thesis, room temperature and hot tensile tests are adopted to address the problem experimentally. The damage evolution mechanisms is defined at various temperatures and a micromechanics based model of the Gurson type considering several populations of cavities nucleated by different second phase particles groups is developed on the basis of the experimental observations. This model allows relating quantitatively microstructure and ductility at various temperatures strain rates and stress triaxialities. Finite element simulations based on an enhanced micromechanics-based model are used to validate the model. Finally, the effect of some key factors that determine the extrudability of aluminium is also discussed and a correlation between the ductility calculations in uniaxial tension and the maximum extrusion speed is developed for one defined profile.

This thesis deals with pre-treatment of surface of aluminium alloys. The theoretical part focuses on the properties of aluminium and its alloys, on methods of surface treatment and the possibilities of quality assessment of pre-treated surface. The experimental part deals with finding of a proper method of pre-treatment. The quality of surface pre-treatment is assessed by observation by SEM with EDS and by single lap shear tests of adhesive joints. According to evaluated results, the optimalised methods are qualitatively and financially compared with the commercial method.

Aluminum alloys are of great importance in the automotive and truck industries due to the weight savings that they can help to achieve. However, the use of such alloys in applications where they are subjected to alternating stresses requires knowledge about their fatigue behavior. Moreover, extrusion induces a strong texture and microstructural heterogeneity in the material and gives a surface with long grooves parallel to the extrusion direction (ED), so-called die lines. This anisotropy in surface conditions and microstructure may affect the fatigue properties. To investigate how die lines and microstructure affects fatigue in aluminum, the high cycle fatigue properties cycles of three peak-aged AlMgSi alloys were evaluated. Flat profiles of 6060-T6, 6063-T6 and 6082-T6 were tested in uniaxial stress (R = 0.1) in a servo-hydraulic fatigue testing machine with a constant stress amplitude. Two specimen types were tested for 6063 and 6082: one with the ED parallel to the loading direction (longitudinal), and one with the ED perpendicular to it (transverse). It was found that both 6063 and 6082 displayed anisotropy in fatigue lives, with the longitudinal orientation performing better. The anisotropy was far stronger in 6082 than in 6063. Furthermore, 6060 longitudinal displayed higher fatigue strength than 6063 longitudinal at higher stress amplitudes, but lower fatigue strength at lower amplitudes. Metallographic investigations with SEM indicated that grain boundaries of the surface-layer grains were involved in the initiation of the fatigue crack. Intergranular crack propagation and separation was observed on the fracture surfaces, especially in the surface layer. The extruded surfaces also showed evidence of intergranular crack propagation. The exact sites of crack initiation could not be found so it could not be proven conclusively that die lines were sites of crack initiation in transverse specimens, but there were some indications from metallographic and macrofractographic investigations that this was the case. / Aluminiumlegeringar används mycket i bilindustrin på grund av de viktbesparingar som kan åstadkommas. Användandet av sådana legeringar i tillämpningar där det utsätts för cykliska laster kräver dock kunskap om deras utmattningsbeteende. Dessutom skapar extrusionsprocessen en stark textur och heterogenitet i mikrostrukturen och resulterar i en yta med fina fåror parallella med pressriktningen, s.k. die lines. Anisotropin i ytbeskaffningen och mikrostrukturen kan påverka utmattningshållfastheten. För att undersöka hur die lines och mikrostruktur påverkar utmattningen i aluminium testades högcykelutmattningsegenskaperna hos tre toppåldrade AlMgSi legeringar. Platta profiler av 6060-T6, 6063-T6 och 6082-T6 testades i enaxlig dragspänning (R = 0.1) i en servohydraulisk utmattningsmaskin med konstant lastamplitud. Två sorters provstavar testade av 6082 och 6063: en med pressriktningen parallell med lastriktningen (längsriktning) och en med pressriktningen vinkelrät mot lastriktningen (tvärriktning). Både 6063 och 6082 uppvisade olika utmattningsliv beroende på pressriktningens orientering mot lastriktningen, där längsriktningen hade längre utmattningsliv för båda legeringarna. Anisotropin var mycket starkare in 6082 än 6063. Dessutom uppvisade 6060 i längsriktningen högre utmattningsstyrka än 6063 vid höga lastamplituder, men lägre utmattningsstyrka vid lägre lastamplituder. Metallografiska undersökningar med SEM indikerade att korngränser i ytlagret var involverade i sprickinitieringen. Spricktillväxt i och separation av korngränser observerades på brottytorna, speciellt i ytlagret. Den extruderade ytan visade också bevis för interkristallin spricktillväxt. De exakta platserna för sprickinitering kunde inte hittas så det kunde inte entydigt bevisas att sprickinitieringen skedde i die lines i provstavar med pressriktningen vinkelrät mot lastriktningen, men i metallografiska och fraktografiska undersökningar fanns vissa indikationer att så var fallet.