Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
  • C22C21/06—Alloys based on aluminium with magnesium as the next major constituent
  • C22C21/08—Alloys based on aluminium with magnesium as the next major constituent with silicon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
  • C22C21/06—Alloys based on aluminium with magnesium as the next major constituent

Definitions

• the present invention relates to aluminium alloys containing magnesium and silicon in the general range of 0.3 to 1.2 weight %-Mg and 0.2 to 1.2 weight Si.
• An alloy of this type containing OAS-0.9% Mg and 0.20.6% Si is the most widely used for the production of aluminium extrusions.
• This alloy is widely known under the Aluminum Association Standards as Alloy 6063.
• Other alloys with different ranges of Mg and Si or the addition of small amounts of other elements are' widely used for the production of aluminium extrusions. Similar alloys are in use in other countries, although the chemical composition limitsmay differ slightly from those registered with The Aluminum Association. I
• the alloying elements and the impurities present in the extrusion ingot are either in solid solution in the aluminium matrix or segregated in the form of intermetallic'phases at the boundaries of the grains into which the alloy has solidified, or at the boundaries of the dendrite cells within thosegrains. It has been common practice for some years to homogenise the structure of 6063 alloy by a heat treatment aimed at eliminating coarse particles of the magnesium silicide phase and the micro-segregation or coring of magnesium and silicon in the dendrite cells, since it is not possible to obtain the optimum properties or extrusion speeds in extrusions produced from ingots containing such segregation of magnesium and silicon.
• the as-cast ingots are heated for several hours at a temperature of about 550C. and cooled rapidly so as to lock a large proportion of the magnesium silicide in solution and to ensure that the remainder of this phase is precipitated in the form of very finely dispersed particles.
• Extrusions with very good mechanical properties can be produced at favourable extrusion pressures and speeds if ingots homogenised in this way are reheated quickly to the extrusion temperature.
• the surface finish'of extrusions produced from such ingots is not always as good as is desired.
• the surface finish of an extrusion is to a large extent dependent on the speed at which the metal is forced past the die. It is an object of the present invention to provide an improvement of the Alloy 6063 composition and of like Al-Mg-Si alloys having magnesium and silicon levels in the ranges referred to above, which permits an increase in the extrusion rate without loss of surface finish of the extrusion or conversely to provide a better standard of surface finish without change of extrusion rate as compared with a typical specimen of Alloy 6063 coming within the general specification.
• a principal cause of defects in the quality of the surface finish of Alloy 6063 extrusions is the breaking away of solid components from the surface of the metal as it is forced through the die orifice. These defects manifest themselves as light-coloured micro score-lines or tears on the surface of the extrusion and are commonly referred to as pick-up. Generally, the incidence of pick-up and its deleterious effect on the reflectivity and smoothness of the surface of the'extruded metal increase with the extrusion speed.
• B-Al-Fe-Si intermetallic phase
• This phase which is insoluble under the normal homogenisation conditions referred toabove, grows in the form of thin, brittle sheets and is formed during the production of the ingot by the direct chill, casting process.
• the B-Al- Fe-Si is.believed to have the chemical formula Fe -Si Al and has a monoclinic type crystal structure.
• the insoluble Fe-rich phase can also be present in a different form, a-Al-Fe-Si, This phase is believed to have a chemical formula Fe -Si-Al, and has a cubic type crystal structure. It has now been found that substantial re duction in pick-up defects can be achieved if the Al-Fe- Si phase present in the ingot during extrusion is in the oZ-phase, believed to be because it is less mechanically brittle'than the B-form. This is particularly true whilst the level of iron in the alloy is maintained within the range of 0.050.3%. Above 0.3 Fe pick-up tends to increase, irrespective of the phase of the aluminiumiron-silicon intennetallic compound, whilst below 0.05% Fe the iron-rich phases are not detrimental to the surface quality of the extruded section.
• the addition of strontium or calcium in amounts of 0.01-0.5% in aluminiummagnesium-silicon alloys of the type under discussion results in at least a major proportion of the Al-Fe-Si phase in the as-cast ingot being in the a-phase.
• Other elements can be tolerated in the alloy in substantial amount;
• the alloy may contain up to 0.4% Cu, up to 0.1% each of Mn and Zn and a total of up to 0.15% (0.05% each)'of additional impurities without losing the benefits arising from the Ca or Sr addition.
• addition of calcium or strontium in amounts of 0.01 to 0.5% is envisaged, most of the benefits of the invention are obtained by an addition of about 0.02-0.05%.
• Sr or Ca in an amount of about 0.05% substantially the whole of the Al-Fe-Si phase is in the a-form in the as-cast ingot.
• higher extrusion rates may be achieved by heating the ingot above the Mg si solvus temperature for sufficient time to bring the Mg Si phase into solution.
• the level of the Sr or Ca addition is preferably held at about 0.020.05% because substantially the whole of the benefit of the addition has been achieved at that level.
• One alloy according to the invention had the following composition: Si 0.400.50%, Mg 0.450.55%, Fe 0.150.25%; Sr or Ca 0.01 50.05%; total other impurities 0.2% (max), Al balance.
• This alloy was cast into round extrusion ingots by the DC. casting process and the ingots were heat treated at temperatures between 500 and 580C, for about 1 hour, to solutionise the magnesium silicide.
• this material was extruded it was found that there was a significant improvement in the specular reflectivity and smoothness of the extrusions as compared with the extrusions of the same alloy (but without either the Sr or Ca addition).
• this alloy containing 0.0 l 8% Ca (a), and 0.05% Ca (b), was compared with the standard, Ca-free, alloy (c).
• the ingots were extruded, after reheating to 425C, at 150 ft./min. with the following results:
• An as-cast aluminium magnesium silicide alloy extrusion ingot containing Al-Fe-Si said alloy consisting essentially of 0.3-1 .2% Mg, 0.2-1.2% Si, up to 0.4% Cu and up to 0.1% each Zn, Mn, ODS-0.3% Fe as impurity and 0.15% total (0.05% each) other impurities, balance aluminum, characterized by the presence of Sr and/or Ca in a total amount of 0.0 l-0. 5% for causing at least a major proportion of the Al-Fe-Si in the as-cast ingot to be in the a phase, thereby to reduce pickup upon extrusion of the ingot.
• a homogenized aluminium magnesium silicide alloy extrusion ingot containing Al-Fe-Si said alloy consisting essentially of 0.3-1 .2% Mg, 0.2-1.2% Si, up to 0.4% Cu and up to 0.1% each Zn, Mn, 0.050.3% Fe as impurity and 0.15% total (0.05% each) other impurities, balance aluminium, characterized by the presence of Sr and/or Ca in a total amount of 0.0 l0.5%; at least a major proportion of the Al-Fe-Si in the ingot being in the a phase, thereby effecting reduction in pickup upon extrusion of the ingot.
• An aluminium alloy ingot extrusion containing Al- Fe-Si said alloy consisting essentially of 0.3-1.2% Mg, 0.2-1.2% Si, 0.010.5% of an alloying element selected from the class consisting of Sr and Ca, 0.050.3% Fe, up 'to 0.4% Cu, up to 0.1% each of Zn and Mn, 0.15% total (0.05% each) other impurities, balance Al, characterized by being essentially free from pickup and having good specular reflectivity, image clarity and whiteness; at least a major proportion of the Al-Fe-Si in the extrusion being in the a phase.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Extrusion Of Metal (AREA)
• Photoreceptors In Electrophotography (AREA)
• Vehicle Body Suspensions (AREA)
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Citations (3)

• 1972
  • 1972-08-23 GB GB3935572A patent/GB1430758A/en not_active Expired
• 1973
  • 1973-07-31 IT IT27330/73A patent/IT992774B/it active
  • 1973-08-09 US US386992A patent/US3926690A/en not_active Expired - Lifetime
  • 1973-08-14 CA CA178,744A patent/CA993688A/en not_active Expired
  • 1973-08-17 DE DE19732341689 patent/DE2341689A1/de active Pending
  • 1973-08-21 CH CH1201973A patent/CH608522A5/xx not_active IP Right Cessation
  • 1973-08-22 NL NL7311573A patent/NL7311573A/xx not_active Application Discontinuation
  • 1973-08-22 ES ES418116A patent/ES418116A1/es not_active Expired
  • 1973-08-22 NO NO3323/73A patent/NO134663C/no unknown
  • 1973-08-22 BE BE134822A patent/BE803892A/xx unknown
  • 1973-08-23 JP JP48093912A patent/JPS4986207A/ja active Pending
  • 1973-08-23 FR FR7330597A patent/FR2197074B1/fr not_active Expired

Patent Citations (3)

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