JPS60145365A - Manufacture of al-zn-mg alloy having superior weldability and resistance to stress corrosion cracking - Google Patents

Abstract

PURPOSE:To obtain an Al-Zn-Mg alloy having superior weldability and resistance to stress corrosion cracking by specifying the composition of an Al-Zn-Mg alloy and conditions during the treatment and working of the alloy. CONSTITUTION:An Al alloy consisting of, by weight, 3.0-8.0% Zn, 0.3-3.0% Mg, 0.005-0.20% Ti, 0.0005-0.05% B, >0.5-1.5% Ni, one or more among 0.03-0.5% Cu, 0.03-0.5% Ag and 0.2-0.7% Si, one or more among 0.05-0.40% Mn, 0.05-0.40% Cr and 0.05-0.25% Zr, and the balance Al is melted and cast. The grain size of the resulting ingot is reduced to <=1,500mum, and the ingot is homogenized at 400-550 deg.C and hot worked at 350-500 deg.C and >=60% reduction of area. It is then subjected to final heat treatment so as to adjust the ratio between the minor and major axis sizes of the grains to 1:>=5 and the minor axis size to <=80mum.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an Al-
The present invention relates to a method for manufacturing a Zn-Mg alloy.

In general, AIZnMg-based alloys have excellent mechanical properties and weldability, and are therefore widely used in railway vehicles and various land structures.

This kind of high-strength A1 alloy is prone to stress corrosion cracking as the strength increases, and AI Zn Mg
These alloys are no exception, and Mg and Zn are added to increase their strength.
As the content increases, stress corrosion cracking resistance deteriorates.

Furthermore, AI Zn Mg alloy is the material with the highest strength that can be welded among the A) alloys, but as the Mg and Zn contents increase, weldability also deteriorates. This is also the cause of hindering the development of high-strength welded structural materials.

However, with regard to stress corrosion cracking, improvements in ingredients and manufacturing conditions have reduced the possibility of stress corrosion cracking in the parallel and perpendicular directions of plates and sections, but in the thickness direction. Regarding welded parts, stress corrosion cracking may occur depending on the usage conditions.

In recent years, structures have become larger and the design and
In order to streamline construction, the use of thicker materials is increasing, and the stress generated in the plate thickness direction and welded parts is large.
There is a strong demand for improved stress corrosion cracking resistance.

As explained above, the present invention solves various problems in high-strength A1 alloy, and in particular, Al-Zn-Mg which has excellent weldability and Ilj; I stress corrosion cracking resistance.
The present invention provides a method for manufacturing an alloy.

A with excellent weldability and stress corrosion cracking resistance according to the present invention
The characteristics of the manufacturing method of IZ, n-Mg alloy are as follows:
Zn3.0~8.0t%, MgO, 3~3.0t% 1%
, Ti 0.005-0.20+ut%, BO,00
05~0.05 t%, Ni 0.5~1.5+ut%
(excluding 0.5u+t%) and CLl
0.03-0.5t%, Ag0.03-0.51%, S
Mn 0.05-0.40u+t%,
CrO, 05-0, 40+ut%, Zr0.05-0
．． The crystal grain size of A1 alloy containing one or more selected from 25+u1% and the balance A1 and impurities is 150%.
The ingot refined to 0 μm or less is heated at 400 to 550'C.
After homogenization at a temperature of 350...500°
After the final heat treatment, the ratio of the short axis to the long axis of the crystal grains is 1:5 or more.
1- The length of the short axis should be 80μIl+ or less when closing.

A with excellent weldability and stress corrosion cracking resistance according to the present invention
The I Zn P = Junkin alloy manufacturing method improves stress corrosion cracking resistance without impairing weldability. In other words, stress corrosion cracking is a type of brittle fracture that occurs at grain boundaries. The initial cause of this phenomenon is said to be preferential elution of grain boundaries due to the potential difference between grain boundaries and within grains.Increasing the Mg, Zn content increases the strength, but the Since the potential difference increases, stress corrosion cracking becomes more likely to occur, but Ni content prevents preferential elution of grain boundaries and has the effect of improving stress corrosion cracking resistance. , even the inclusion of Si alone improves resistance to corrosion and cracking, and as the content increases, welding and Vl-
begins to deteriorate. Therefore, Cu, Ag, Si
By repeatedly containing one or more selected from the following in small amounts in combination, stress corrosion cracking resistance can be significantly improved without deteriorating weldability.
1. B is an important element for the refinement of M, and its inclusion improves weldability, and furthermore, M n, C
r and Zr are elements for stabilizing the structure.

In addition, as the Mg and Z++ contents increase, the melting temperature at the grain boundaries decreases, so cracking at the grain boundaries becomes more likely to occur due to temperature differences during welding and shrinkage stress during solidification.
The crystal grain size of the ingot is refined to 1500 μm or less, and
For example, after homogenization treatment for 1 to 24 hours at a temperature of ~550'C, hot working of 60% or more is performed at a temperature of 350 to 500°C to reduce the ratio of the short axis to the long axis of the crystal grains to 1: 5 or more
1- Weldability is improved by setting the short axis length to 80μTo or less.

The method for manufacturing an AI-Zll-Mg alloy having 4-T superior weldability and stress corrosion cracking resistance according to the present invention (hereinafter simply referred to as the manufacturing method according to the present invention) will be described.

First, 1 to 1-Z used in the production method according to the present invention
The content and proportion of the n-Mg alloy will be explained below.

(2' and 11 are for strength) - the most important elemental text for stirring, and if the content is less than 3.0w1% γBi, sufficient strength cannot be obtained, and 8.0+ut If the Zn content exceeds 3.0% to 8.0%, stress corrosion cracking is likely to occur. Therefore, the Zn content is set to 3.0-8.0IIIt%.

Like Zn, Mg is an important element for strength.
If the content is less than 0.3IIIt%, sufficient strength cannot be obtained, and if the content exceeds 3.0IIIt%, stress corrosion cracking is likely to occur. Therefore, the Mg content is 0.
3 to 3.0 IIIt%.

Ti and B are important elements for refining the structure of the ingot, and if the T1 content is less than 0.005u+j% and the B content is less than 0.00051%, there is no effect on grain refining, and Ti 0.20+ut% and B 0.05u
If the content exceeds +t%, there is a possibility that giant compounds will be generated. Therefore, the Ti content is 0.005 to 0.20
...t% and B content are 0.0005 to 0.05u+t
%.

Ni is an element that improves stress corrosion cracking resistance.
When the content of LI, Sl, and Ag is small, this effect is small, and when the content exceeds 1.5 urt%, weldability deteriorates. Therefore, the Ni content is 0.5
~1.5u+1%, and 0.5 side t% shall not be included.

By containing one or more of Cu, Ag, and Si selected from these, the stress corrosion cracking resistance can be improved.
However, the content is CLIo, less than 03d%, Ag 0
If the content is less than 0.003u+j% and Si is less than 0.2u+j%, there will be no such effect even if they are contained in combination and overlappingly.
LIo, 5Tan L%, Ag 0.5+ut%, Si0.7
If the content exceeds t%, weldability deteriorates. Therefore, Cu content is 0.03/0.5...1%, At (content is 0.03~0.5u+t%, 81 content is 0.2~0
, 7u+t%.

Mn, Cr, Zr1. L41 It is an element necessary for weave stabilization, and the crystal grains are finely controlled by homogenization and hot working, but the content is Mn 0005u+1
%, Cr 0.05u+1%, Zr 0.05
There is no effect on the skin at less than LIII%, and Mn is less than 0.
40wt%, CrO, 40+01%, ZrO, 25
If the content exceeds +ut%, there is a possibility that giant compounds will be generated. Therefore, M1] content 1j: 0.05-
0.40+ut%, Cr content 1. t 0105-0.
40u+1%, Zr content is 0.05-0.25+ut
%.

AI-Zn-M with such components and component ratios,
The crystal grain size of the ingot made by melting the alloy is 1500μ.
It is refined to less than m0, and the crystal grain size is 1500 μm.
If it is larger than m, the grain size of the product increases and weldability deteriorates, so the grain size of the gj lump must be 1500μ[)1 or less.

Next, heat treatment will be explained.

"The ingot of item 1 is heated at a temperature of 400 to 550'C, for example,
Homogenization treatment is carried out for 1 to 24 hours, but 400
At temperatures below 550°C, the precipitation of Mn, C, r, and Zr is insufficient and the crystal grains of the product become enlarged, and at temperatures above 550°C, the precipitates of Mn, Cr, and Zr solidify again. When melting begins, even if the crystal grains of the ingot are fine, the crystal grain size of the product increases and weldability deteriorates.

After this homogenization treatment, the M
Dislocations are finely and uniformly distributed in a metastable form using precipitates of n, Cr, and Zr as nuclei, and the ratio of the short axis to the long axis is set to 1:5 or more in the recrystallization process in the subsequent process such as solution treatment and quenching. Second,
In addition, the length of the short axis is controlled to be 80 μm'QJ or less.

However, hot processing such as hot rolling, hot extrusion, and hot forging is difficult at low temperatures below 350°C.
At high temperatures exceeding 500°C, there is a possibility of thermal open cracking, which increases the crystal grain size of the product and deteriorates weldability. Also,
If the processing rate is less than 60%, the crystal grain size of the product will increase, and furthermore, if the ratio of the short axis to the long axis of the final product is less than 1:5 and the short axis is larger than 80μ. Weldability becomes poor.

A with excellent weldability and stress corrosion cracking resistance according to the present invention
An example of a method for producing an I-Zn-MB alloy will be described together with a comparative example.

Example AI-Zn-M with the components and component ratios shown in Table 1
An ingot produced by melting and casting Alloy B by a conventional method was treated under the following conditions.

(1) Conditions for the manufacturing method of the AI-Zn-M alloy with excellent weldability and stress corrosion cracking resistance according to the present invention (A) After homogenization treatment for 24 hours at a temperature of 450 ° C.
By performing 90% hot rolling at a temperature of 450'C, 25
A board of mm[ was manufactured.

(2) Comparative conditions (B) After homogenization treatment at a temperature of 570°C for 24 hours, 450-5
25% by hot rolling at a temperature of 00°C.
A plate material of l1lI111 was manufactured.

These plates were subjected to solution treatment at a temperature of 450° C. for 30 minutes, then cooled with water, and aged at a temperature of 120° C. for 24 hours.

Table 2 shows the results of investigating the properties of this board shrine.

1) Grain size: Observation of cross sections parallel to the longitudinal direction of plates and shapes.

2) Stress corrosion cracking resistance: Stress was applied in the thickness direction using a C-R1n8 test piece,] 3g/lNa of OC1'C
It was immersed in a mixed aqueous solution of C1-30H/lK and cr20736g/1cro3.

Oα: No cracking at 0 minutes, ×a: Cracking occurred at 0 minutes.

3) Slit type crack test: A slit type weld crack test piece with a thickness of 1.2 m+nl was used.

Cracking % = (Crack length/Full length of weld) x 1. O (1 Filler metal 5356 Current 280A Voltage 30V 4) Micro fin shear: Observe the vicinity of the weld of the butt weld material.

Thickness 6+n+nl Filler metal 5356 Current 26 +') A Voltage 30V Test conditions 10 (1'C 3g/lNaCl-36g/1cro
,, -30 g/l K2Cr2O7 mixed aqueous solution was immersed and cracks were observed.

As is clear from Table 2, the plates manufactured under the conditions of the present invention (A) have superior weldability and better stress corrosion cracking resistance than the plates manufactured under the comparative conditions (B). It turns out that it is excellent.

Claims (1)

[Claims] Zn 3. G-8,0wt%, IVf 0.3-3.0
+ut%, TiO, 005-0,20u+1%, B O
,0005-0,05u+t%,Ni005~1,5u
+t% (excluding 0.5t%), and Cu
O, 03-0, 5u+t%, A go, 03-0.5
11It%, S10.2~0.7u+t%, and Mn 0.05-0.
40+u1%, CrO, 05-0,40u+t%, Z
An ingot containing one or more selected from r0.05 to 0.25...t% and having a refined crystal grain size of A1 alloy consisting of the balance A1 and impurities to 1500 μτ11 or less is 40
After homogenization treatment at a temperature of 0 to 550 °C, 35
Hot working is carried out at a temperature of 0 to 500°C with a processing rate of 60% or more, and the ratio of the short axis to the long axis of the crystal grains after the final heat treatment is 1:
5 or more, and the length of the minor axis is 80 μm or less.