| 摘要 |
1,169,056. Making pistons; altering physical properties. ALUMINUM CO. OF AMERICA. 18 Oct., 1967 [25 Oct., 1966], No. 47523/67. Headings B3A and B3V. [Also in Division C7] The fatigue strength of an aluminium or aluminium alloy casting is improved by subjecting the casting to a substantially isostatic pressure of at least 3000 p.s.i. while maintaining the casting at a temperature of at least 600‹F. but less than the melting point of the metal for a time sufficient to render the casting substantially free from micropores over 0À0001 inch in size. Tensile strength also is improved, and pressures up to 100,000 p.s.i. and temperatures up to 1000‹ F. are referred to. Application times range from several seconds to more than an hour. The pressure may be applied by dies or fluid, e.g. helium gas. A casting may be quenched immediately after treatment, followed by an artificial ageing. Alternatively, a separate heat treatment may be applied after the isostatic pressure treatment. A rough sand casting may be machined, improved by the isostatic treatment, heat treated and then finish machined. In an example, an aluminium alloy piston casting including 4¢% Cu, 1¢% Mg and 2%Ni, was heated to 850‹ F. and placed in a preheated die. A ram was forced against the piston for 1¢ minutes at 47,000 p.s.i. In a further example the piston had a Ni-Fe ring insert. In another example specimens from an aluminium alloy casting containing 9% Si, ¢ Mg and 1À8% Cu were treated isostatically, after which they were reheated to 980‹ F. for 8 hours, quenched in water at 150‹ F. and artificially aged for 10 hours at 310‹ F. |
