Morphological analysis of SSM Al-4.5wt.% Cu measured by the rheocast quality index
Abstract There is a direct relationship between grain size obtained from macrostructure characterisation and the globule size and shape factor, obtained from microstructure characterisation: the smaller the grain size, the smaller the globule size and shape factor. Due to this a rheocast quality index ( RQI = globule size /( grain size × shape factor) ) was used to evaluate the Al–4.5 wt.% Cu alloy produced by strain induced melting activation (SIMA). The structure that presents the smallest grain size, the smallest shape factor, and the most homogeneous and globular size of the primary phase, has the best RQI and consequently the best behaviour in the semi-solid forming. Four different as-cast structures were cold rolled to obtain 20 and 40% deformation and were partially melted at 635 °C at holding times of 5 min. Both, macro- and microstructure were characterised.
AA2024 ALAŞIMINDA SIMA YÖNTEMİ İLE TİKSOTROPİK YAPI ÜRETİMİ ÜZERİNE YENİDEN ISITMA SICAKLIĞININ ETKİSİ
Bu calismada, bir dovme aluminyum alasimi olan AA2024 alasiminda gerinimin neden oldugu sivi aktivasyonu(strain induced melt activated-SIMA) yontemi ile yari-kati sekillendirme icin gerekli tiksotropik mikroyapiuretimi arastirilmistir. Bu amacla ekstruze halde AA2024 alasimi %20 oraninda soguk deformasyona tabitutulmus ve takiben %30, %40 ve %50 sivi oranina karsilik gelen yari-kati sicakliklara isitilarak oda sicakliginasahip suda sogutulmustur. Mikroyapi analizleri metalografik inceleme ve nicel olcum yontemleri ile yapilmistir.Deneysel sonuclar, SIMA yontemiyle AA2024 alasiminda, yari kati sekillendirme icin gerekli olan kureselsekilli tiksotropik mikroyapilarin uretilebilecegini gostermistir. Artan yari-kati sicaklikla tane boyutu artarkensekil faktorunde belirgin bir degisim gozlenmemistir. SIMA yontemi ile tiksotropik yapi uretimi icin yari-katisicakliklarda izotermal bekletmeye gerek olmadigi tespit edilmistir.
Some Chemical and Physical Properties of Rubber
The chemical constitution and physical state of natural rubber in its viscous, high-elastic and crystalline conditions are described. It is shown that those depend on long hydro-carbon chains which are normally coiled and tangled. The high elasticity of rubber is made possible by the ability of the chains to straighten and recoil. On breaking down the cohesion between the chains by various means, rubber has some of the characteristics of a thick oil; whilst, on the other hand, certain conditions, especially those of intense cooling, cause rubber to behave in many respects like a crystalline material. This concept is then extended to a consideration of other rubber-like materials including gutta percha, some synthetic elastomers and finally the silicone rubbers.