Aluminium alloy base plate for magnetic disk and production method thereof

Abstract

The invention relates to an aluminum alloy substrate having excellent strength and improving surface smoothness of a disk plated by NiP and a manufacturing method thereof. The aluminum alloy substrate for the disk uses a sheet continuously casting method to manufacture molten metal of aluminum alloy into a plate; the aluminum alloy contains 3.5 to 15 weight percent of Mg, 0.01 to 0.1 weight percent of Si, 0.01 to 0.1 weight percent of Fe, 0.02 to 0.35 weight percent of Cr, and at least one of Cu and Zn with stated amount; at a high temperature ([Mg]: Mg content (weight percent) in the aluminum alloy) of between 300 DEG C and (14.7x[Mg]+2.4) DEG C or more, the blanking processed plate is pressurized and annealed, and then leveled by cooling at an over stated speed; and the aluminum alloy substrate for the disk is characterized in that the maximum length of a compound of metals between Al and Fe series on the surface is below 7 microns, the maximum length of a compound of metals betweenMg and Si series on the surface is below 4 microns, and area occupation ratio of an Al3Mg2 is below 1 percent.

Description

Aluminum alloy substrate for magnetic disk and manufacturing method thereof technical field The present invention relates to a substrate made of aluminum alloy which is attached with a magnetic film to form a magnetic disk, and a method for manufacturing the same. Background technique Magnetic disks used as recording media for computers and the like are formed by attaching a magnetic film to a non-magnetic substrate. Generally speaking, since the substrate is required to be lightweight, have high rigidity, and have a smooth surface, an aluminum alloy plate is used for reasons such as non-magnetic, lightweight, and easy to obtain a smooth surface by mirror finishing. Obtain rigidity and form a NiP coating film with a thickness of about 10 μm to make a substrate for a magnetic disk. Conventionally, JIS 5086 alloy (Al—Mg alloy) has been used as such an aluminum alloy sheet because it has strength to withstand machining such as mirror finishing and can obtain sufficient surf...

AI Technical Summary

Problems solved by technology

In addition, when the subsequent cooling rate is slow, the β phase may precipitate during cooling.

Moreover, when there is a β phase on the surface of the mirror-finished aluminum alloy substrate (substrate), due to the difference in etching rate with the parent phase in the pre-plating treatment, the portion where the β phase exists becomes a pit, which reduces the thickness of the coating surface. smoothness

Images