Al-Si-Mg alloy

The microstructures of ceramic matrices grown from two different classes of alloys have been reported. The external growth surface of ceramic matrices grown from an Al-Si-Mg alloy in the absence of a reinforcement was covered by a thin ( 1- to 4-gm) layer of MgO that sometimes contained up to 5% MgAl204 [33]. The external MgO layer typically was separated from the interconnected A1203 matrix by a thin aluminum alloy (1- to 3-gm) layer. Only rarely was an A1203 grain found in direct contact with the external oxide layer. Within the bulk of the composite, the metallic channels typically were 3 to 8 /tm in width. 

When a Zn-containing alloy was used to form the composite matrix, the external surface of the growth was covered by a thin layer of ZnO [29]. No ZnAl204 was observed. For these composites, a thin metal layer separating the external ZnO layer from the A1203 matrix was also observed, but it was significantly thinner than the layer found in using Al-Si-Mg alloys. 

The addition of alloying elements can also indirectly affect the oxygen solubility gradient across the thin metallic surface layer by modifying the activity of an element that interacts with Al. For example, Fe forms very stable intermetallics with silicon, while the Fe-Al and Fe-Mg intermetallics are less stable. Additions of Fe to an Al-Si-Mg alloy, therefore, will decrease the Si activity, and thereby increase the Mg activity. This will lead to a lower oxygen potential gradient and a lower growth rate. 

Modifications to Precipitates. Silicon is sometimes added to Al—Cu—Mg alloys to help nucleate S precipitates without the need for cold work prior to the elevated temperature aging treatments. Additions of elements such as tin [7440-31-5] Sn, cadmium [7440-43-9] Cd, and indium [7440-74-6] In, to Al—Cu alloys serve a similar purpose for 9 precipitates. Copper is often added to Al—Mg—Si alloys in the range of about 0.25% to 1.0% Cu to modify the metastable precursor to Mg2Si. The copper additions provide a substantial strength increase. When the copper addition is high, the quaternary Al CuMg Si Q-phase must be considered and dissolved during solution heat treatment. 

M.D. Dighe et al Effect of loading condition and stress state on damage evolution of silicon particles in an Al-Si-Mg-Base cast alloy. Metall. Matls. Trans. A 33, 555-565 (2002)... 

M.F. Horstemeyer et al Modeling stress state dependent damage evolution in a cast Al-Si-Mg aluminum alloy. Theor. App. Fracture Mech. 33, 31 —47 (2000)... 

Materials Glasses Metals — Natural Composites Al alloys 5xxx (Al-Mg) Ni alloys 6xxx (Al-Mg-Si) — Mg alloys 7xxx (Al-Zn) Zn alloys 2xxx (Al-Cu) 6066-T4 6162-T5 6162-T6 6463-Tl Coefficient of expansion a — Corrosion, mm-year Cost (relative cost per unit) Fatigue Corrosion fatigue... 

Al-Si-Mg. Good casting alloys, which can be solution treated and age hardened to give good mechanical properties. 

Mer] Meredith, M.W., Worth, J., Hamerton, R.G., Intermetalhc Phase Selection During Sohdifi-cation of Al-Fe-Si(-Mg) Alloys , Mater. Sci. Forum, 396-402,107-112 (2002) (Phase Relations, Experimental, 9)... 

The corrosion resistance of the Al-Mg-Si alloys is slightly inferior to that of the Al-Mg alloys, but where maximum obtainable strength is required then a fully heat-treated Al-Mg-Si alloy would generally be preferable to an Al-Mg alloy with comparable properties obtained by cold working. 

As seen above Moran et a ., has commented upon the exfoliation corrosion of Al-Li-Cu-Zr-Ge . The mechanism has been investigated by Reboul and Bouvaist and a mathematical model suggested by Robinson . The influence of alloy elements in Al-Zn-Mg has been reported by Reboul and it has been shown that exfoliation corrosion of Al-Mg-Si in irrigation water is also governed by alloy and impurity concentration . 

Stress-corrosion cracking occurs in certain aluminium alloys which have been developed for medium and high strength by employing variations in composition, cold work and heat treatment The main alloys are based upon Al-Mg, Al-Mg and Al-Cu, but stress corrosion also occurs in Al-Ag, Al-Cu-Mg, Al-Mg-Si, Al-Zn and Al-Cu-Mg-Zn alloys. It has... 

Al-Mg (5000 Series) and Al-Mg-Si (6000 Series) In the binary alloy system strength is obtained mainly by strain hardening. Stress corrosion is thought to be associated with a continuous grain boundary film of Mg,Alg which is anodic to the matrix . Air cooling prevents the immediate formation of such precipitates, but they form slowly at ambient temperatures. Thus only low Mg alloys are non-susceptible (Al-3% Mg). Widespread precipitation arising from plastic deformation with carefully controlled heat-treatment conditions can lower susceptibility. Al-5Mg alloys of relatively low susceptibility are subjected to such treatments. Mn and Cr... 

Fig. 20.33 (top) Transmission electronmicrograph showing dislocation tangles associated with precipitates in an Al-Cu-Mg-Si alloy (x 24 000, courtesy S. Blain) and (bottom) light micrograph showing slip lines in pure lead (x 100)... 

The Aoki group [218] has been developing intermetallic alloys based on a CaSi compound that is alloyed with Si, Al, Ge, Mg, and Sr. However, the alloys cannot compete with the LaNi -type or even TiFe because they absorb only slightly more than 2 wt.%H at 100°C and desorb at 200°C. 

When wet Stainless steels are unaffected Al si affected Cu, brass, Mg, Mg-Al alloy, mild steels are considerably affected Power by Ballistic Mortar Test — 119% TNT Power by Trauzl Test — 120% TNT Rifle Bullet Impact Test — Burned 7%, Unaffected 93%... 

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