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
  • C22C21/02—Alloys based on aluminium with silicon as the next major constituent

Definitions

• Al-Si alloys which have a small strontium content and good technological properties have become known as materials for the construction of highly stressed pistons and cylinder heads.
• Al-Si alloy melts which have been modified with calcium do exhibit a modification effect, which is less than that attained with sodium but of longer duration.
• Al-Si alloys which have been modified with calcium have very serious drawbacks.
• the calcium addition promotes the tendency of the eutectic Al-Si alloys to oxidize to a great degree and the alloys which have been treated with calcium have an unattractive appearance because of their dirty gray surface color (normally treated Al-Si alloys exhibit a metallic lustre) and in addition exhibit a most undesirable oxide skin formation near the gates of castings which in foundry practice is called elephant skin.
• the decisive disadvantage of calcium modified Al-Si alloys is to be seen in that only very rapidly solidified cast parts, for instance, in chill molded castings with a wall thickness of 3 mm. exhibit a pseudo modified structure whereas a lamellar structure occurs at locations of local overheating. The slower the solidification takes place the greater the occurrence of zones of lamellar structure which results in the increased occurrence of shrinkage faults which are typical for lamellar structures. These shrinkage faults are extremely disadvantageous and cannot be avoided by the usual supply measures.
• Al-Si alloy melts which have been modified with calciurn, the modification effects are retained with one remelting procedure, but here again the oxidic influences are increased.
• the invention therefore relates to a process achieving a long lasting modification effect in Al-Si alloys by the introduction of an alkaline earth metal in a small quantity into Al-Si alloy melts.
• this is effected by adding strontium and barium individually or in combination in a quantity of 0.001 to 2.0 wt. percent, preferably, 0.05 to 0.2 wt. percent, to Al-Si alloy melts with 5 to 14 wt. percent of Si and if desired contents of Mg and/or Zn/or Cu and the remainder Al and in addition may contain the usual impurities.
• the effect of the Sr and/or Ba addition according to the invention can be assisted by the addition of Be in a quantity of 0.001 to 2.0 wt. percent, preferably, 0.05 to 0.2 wt. percent.
• the beryllium addition can be simultaneous with or before or after the addition of the Sr and/ or Ba. Whereas beryllium by itself has no modification effect in Al-Si aloys nor has a noticeable or noteworthy effect on the oxidation of Sr and Ba free Al-Si alloys, the simultaneous presence of Be and Sr and/or Ba provides a synergistic effect. The oxidation of Sr is hindered by Be so that no Sr is lost in the melt and the modification effect is maintained for a still longer period of time.
• the process according to the invention has a number of advantages.
• the modification elfect achieved with Sr and/or Ba, if desired, in conjunction with Be, is retained over a long period of time.
• the effect for instance is retained for at least 2 hours and up to 10 hours and in some instances can be retained beyond this range depending upon the quantity of the addition and the temperature at which the molten Al-Si alloys are maintained. It is possible thereby to process large charges of Al-Si alloys either continuously or discontinuously without the necessity of interrupting the processing of the charge to permit further additions of modifying agents.
• Al-Si alloys which have been treated according to the invention can, with especial advantage, also be subjected to degasifying agents or other smelt purifying agents for the production of pore free castings, as such Al-Si alloy melts can be treated with inert or reactive gases for the purpose of eliminating a harmful gas content without the fine grained nature of the alloy being lost on casting.
• Al-Si alloys which have been treated according to the invention are especially well suited for use as construction materials for the production of highly stressed parts which require a high elongation, for example, parts which have an elongation over 10%, a tensile strength of over 19 kg./mm. and a yield point of over 9 kg./mm.
• Al-Si alloys treated according to the invention can also be used in the construction of parts requiring a high tensile strength and high yield point and must have a tensile strength of over 36 kg./mm. a yield point of 32 kg./mrn. with an elongation of 3%.
• Al-Si alloys such as, for example, one of 7 wt.
• the Al-Si alloys treated according to the invention especially when they have been subjected to age hardening, have good further processing properties. They therefore are suited for parts which must be subjected to a fine finishing operation involving a shaving removal action, such as, for example, valve housings and armature parts, the valve seats of which must exhibit a smooth surface.
• Tablets consisting of a mixture of 67% SrCO and 33% Mg powder were introduced into 8.5 kg. of a melt 5 of an Al-Si alloy containing 12% Si at 700 C.
• the strontium content of the mixture introduced was 0.3%.
• Samples cast at 720 C. after the treated melt had been held for 4 hours at 720 C. exhibited a very good modified structure.
• Example 3 In order to ascertain the flow qualities and Al-Si alloy with 9.7% Si and the usual impurities was prepared. Three samples of the same quantity were cast into a special mold according to Ph. Schneider at 720 C. and the length of the spiral of the alloy cast measured.
• the first sample which was given no modification treatment, resulted in a spiral casting 103 cm. long.
• the second sample which was treated with an A1 prealloy containing 5% of strontium to provide a 0.1% content in the melt resulted in a spiral casting 104 cm. long.
• the third sample which was treated with a usual commercial Na modification salt resulted in a spiral casting 81 cm. long.
• Example 4 Tensile Yield Brinell strength, point, Elongation, hardness, kg/mm. lrgJmm. percent kgJmmfl Sand mold 25. 8 24. 0.5 106 Chill mold 30.6 25.4 3.4 107
• Example 5 0.10% metallic strontium were alloyed with an alloy of the composition Percent Zn 9.7 Mg 0.36 Al Remainder at 760 C. The molten alloy was held at this temperature for 4 hours and was then cast in chill molds. After 12 days cold hardening the rods thus obtained had the following mechanical properties Tensile strength "kg/mm? 30.6
• Example 6 0.10% metallic strontium were alloyed with an alloy of the composition Percent Si 8.6
• the rods were free of oxide skins.
• a process for attaining a long lasting modification effect in aluminum silicon alloy-s comprising forming a melt containing aluminum and from 5 to 14 wt. percent silicon, and adding to said melt strontium or barium salts mixed with a finely divided reducing metal selected from the group consisting of aluminum and magnesium.
• strontium or barium comprising from 0.001 to 2.0 wt. percent.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
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• Organic Chemistry (AREA)
• Manufacture And Refinement Of Metals (AREA)

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• 1966
  • 1966-01-13 DE DEM67990A patent/DE1255928B/de active Pending
  • 1966-12-30 NL NL6618414A patent/NL6618414A/xx unknown
• 1967
  • 1967-01-06 LU LU52759D patent/LU52759A1/xx unknown
  • 1967-01-09 FR FR90404A patent/FR1507664A/fr not_active Expired
  • 1967-01-11 GB GB0644/67A patent/GB1169104A/en not_active Expired
  • 1967-01-11 BE BE692488D patent/BE692488A/xx unknown
  • 1967-01-12 US US608754A patent/US3466170A/en not_active Expired - Lifetime

Patent Citations (4)

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