tailieunhanh - Volume 18 - Friction, Lubrication, and Wear Technology Part 21

Tham khảo tài liệu 'volume 18 - friction, lubrication, and wear technology part 21', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | HI IM Fig. 3 Microstructure of type hypereutectic alloy. a Unrefined Graff-Sargent etch . Dark regions contain coarse primary silicon particles in addition to eutectic silica. b Refined as polished . 120X Commercial aluminum-silicon alloys Table 1 generally contain other alloying elements to further enhance or modify the wear resistance or impart additional properties to these alloys. Iron. The most common alloying element is iron which can be tolerated up to levels of to Fe. The presence of iron modifies the silicon phase by introducing several Al-Fe-Si phases. The most common of these are the I and phases. The I phase has a cubic crystal structure and appears in the microstructure as a Chinese script eutectic. The less common phases generally appear as needles and or platelets in the structure. Other iron-bearing phases such as Al6Fe and FeAl3 can also be found in these alloys. Aluminum-silicon alloys intended for die castings typically have higher minimum iron levels to reduce sticking between the mold and the casting. Magnesium is added to provide strengthening through precipitation of Mg2Si in the matrix. In an Al-Fe-Si-Mg alloy the Al-Si-Fe phases will not be affected by the addition of magnesium. However magnesium can combine with insoluble aluminum-iron phases resulting in a loss of strengthening potential Ref 12 . Copper. The most common aluminum wear-resistant alloys also contain copper. Copper additions impart additional strengthening of the matrix through the aging or precipitation-hardening process AlCu2 or Q phase or through modification of the hard brittle Al-Fe-Si phases by substitution in these intermetallic phases. As the strength of these alloys increases through magnesium and copper additions some sacrifice in ductility and corrosion resistance occurs. Manganese. Many of the important aluminum-silicon alloys also contain low 1 wt but significant amounts of manganese. The presence of manganese can reduce the solubility of iron and