Thermal treatment of aluminum base alloy article

Claim 1

THE METHOD OF THERMALLY TREATING ARTICLES COMPOSED OF AN ALLOY CONSISTING ESSENTIALLY OF ALUMINUM, 4.5 TO 14% ZINC, 1.5 TO 3.8% MAGNESIUM, 0.75 TO 2.5% COPPER AND AT LEAST ONE HARDENING ELEMENT SELECTED FROM THE GROUP COMPOSED OF 0.05 TO 0.4% CHROMIUM, 0.1 TO 0.75% MANGANESE, 0.05 TO 0.3% ZIRCONIUM, 0.05 TO 0.3% VANADIUM, 0.05 TO 0.3% MOLYBDENUM AND 0.05 TO 0.3% TUNGSTEN, WHEREIN THE PROPORTION OF MAGNESIUM TO ZINC IS WITHIN THE RANGE OF 0.2 TO 0.5 PART OF MAGNESIUM TO 1 PART ZINC AND THE COPPER CONTENT DOES NOT EXCEED THAT OF MAGNESIUM, SAID TREATMENT COMPRISING HEATING SAID ARTICLES TO A TEMPERTURE BETWEEN 750 AND 1000*F., BUT BELOW THE TEMPERATURE OF INCIPIENT FUSION, FOR A SUFFICIENT LENGTH OF TIME TO PRODUCE SUBSTANTIALLY COMPLETE SOLUTION OF THE SOLUBLE COMPONENTS, QUENCHING SAID ARTICLES TO SUBSTANTIALLY ROOM TEMPERATURE, PRECIPITATION HARDENING SAID QUENCHED ARTICLES IN TWO STEPS ACCORDING TO THE FOLLOWING SCHEDULE: FIRST STEP: FOR ALLOYS CONTAINING LESS THAN 7.5% ZINC, HEATING THE ARTICLES TO 200 TO 275*F. AND HOLDING FOR A PERIOD OF 5 TO 30 HOURS; FOR ALLOYS CONTAINING MORE THAN 7.5% ZINC, HEATING THE ARTICLES TO 175 TO 275*F. AND HOLDING FOR A PERIOD OF 3 TO 30 HOURS; SECOND STEP: HEATING THE ARTICLES TO 315 TO 380*F. FOR A PERIOD OF 2 TO 100 HOURS, THE MINIMUM TIME AND TEMPERATURE RELATIONSHIP TO ACHIEVE HIGH RESISTANCE TO STRESS CORROSION BEING EXPRESSED BY THE EQUATION: T=2.0 + K/(T-280)(**4) WHERE T IS THE TIME IN HOURS, T IS THE PRECIPITATION TEMPERATURE AND K IS A CONSTANT THAT VARIES WITH THE ZINC AND HARDENING ELEMENT CONTENT OF THE ALLOY AND THE THICKNESS OF THE ARTICLE BEING TREATED AS FOLLOWS:

Claim 2

THE METHOD OF THERMALLY TREATING ARTICLES COMPOSED OF AN ALLOY CONSISTING ESSENTIALLY OF ALUMINUM, 4.5 TO 14% ZINC, 1.5 TO 3.8% MAGNESIUM, 0.75 TO 2.5% COPPER AND AT LEAST ONE HARDENING ELEMENT SELECTED FROM THE GROUP COMPOSED OF 0.05 TO 0.4% CHROMIUM, 0.1 TO 0.75% MANGANESE, 0.05 TO 0.3% ZIRCONIUM, 0.05 TO 0.3% VANADIUM, 0.05 TO 0.3% MOLYBDENUM AND 0.05 TO 0.3% TUNGSTEN, WHEREIN THE PROPORTION OF MAGNESIUM TO ZINC IS WITHIN THE RANGE OF 0.2 TO 0.5 PART OF MAGNESIUM TO 1 PART ZINC AND THE COPPER CONTENT DOES NOT EXCEED THAT OF MAGNESIUM, SAID TREATMENT COMPRISING HEATING SAID ARTICLES TO A TEMPERTURE BETWEEN 750 AND 1000*F., BUT BELOW THE TEMPERATURE OF INCIPIENT FUSION, FOR A SUFFICIENT LENGTH OF TIME TO PRODUCE SUBSTANTIALLY COMPLETE SOLUTION OF THE SOLUBLE COMPONENTS, QUENCHING SAID ARTICLES TO SUBSTANTIALLY ROOM TEMPERATURE, PRECIPITATION HARDENING SAID QUENCHED ARTICLES IN TWO STEPS ACCORDING TO THE FOLLOWING SCHEDULE: FIRST STEP: FOR ALLOYS CONTAINING LESS THAN 7.5% ZINC, HEATING THE ARTICLES TO 200 TO 275*F. AND HOLDING FOR A PERIOD OF 5 TO 30 HOURS; FOR ALLOYS CONTAINING MORE THAN 7.5% ZINC, HEATING THE ARTICLES TO 175 TO 275*F. AND HOLDING FOR A PERIOD OF 3 TO 30 HOURS; SECOND STEP: HEATING THE ARTICLES TO 315 TO 380*F. FOR A PERIOD OF 2 TO 100 HOURS, THE MINIMUM TIME AND TEMPERATURE RELATIONSHIP TO ACHIEVE HIGH RESISTANCE TO STRESS CORROSION BEING EXPRESSED BY THE EQUATION: T=2.0 + K/(T-280)(**4) WHERE T IS THE TIME IN HOURS, T IS THE PRECIPITATION TEMPERATURE AND K IS A CONSTANT THAT VARIES WITH THE ZINC AND HARDENING ELEMENT CONTENT OF THE ALLOY AND THE THICKNESS OF THE ARTICLE BEING TREATED AS FOLLOWS: